Fix broken link in README (#700)

Author: mottox2

Diff for: README.md

@@ -116,7 +116,7 @@ export default class Tree extends Component {
 | searchFocusOffset              |     number     | Outline the <`searchFocusOffset`>th node and scroll to it.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |
 | onlyExpandSearchedNodes        |    boolean     | Only expand the nodes that match searches. Collapses all other nodes. Defaults to `false`.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |
 | searchFinishCallback           |      func      | Get the nodes that match the search criteria. Used for counting total matches, etc.<div>`(matches: { node: object, path: number[] or string[], treeIndex: number }[]): void`</div>                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |
-| dndType                        |     string     | String value used by [react-dnd](http://react-dnd.github.io/react-dnd/docs-overview.html) (see overview at the link) for dropTargets and dragSources types. If not set explicitly, a default value is applied by react-sortable-tree for you for its internal use. **NOTE:** Must be explicitly set and the same value used in order for correct functioning of external nodes                                                                                                                                                                                                                                                                     |
+| dndType                        |     string     | String value used by [react-dnd](https://react-dnd.github.io/react-dnd/about) (see overview at the link) for dropTargets and dragSources types. If not set explicitly, a default value is applied by react-sortable-tree for you for its internal use. **NOTE:** Must be explicitly set and the same value used in order for correct functioning of external nodes                                                                                                                                                                                                                                                                     |
 | shouldCopyOnOutsideDrop        |  func or bool  | Return true, or a callback returning true, and dropping nodes to react-dnd drop targets outside of the tree will not remove them from the tree. Defaults to `false`. <div>`({ node: object, prevPath: number[] or string[], prevTreeIndex: number, }): bool`</div>                                                                                                                                                                                                                                                                                                                                                                                 |
 | reactVirtualizedListProps      |     object     | Custom properties to hand to the internal [react-virtualized List](https://github.com/bvaughn/react-virtualized/blob/master/docs/List.md#prop-types)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |
 | style                          |     object     | Style applied to the container wrapping the tree (style defaults to `{height: '100%'}`)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            |