Fix typos in the contributing guide

Just as the contributing guide says: spell check your code.

CONTRIBUTING.md

@@ -2,7 +2,7 @@
 
 By submitting a pull request, you represent that you have the right to
 license your contribution to the Laf project owners and the community,
-agree by submitting the patch that your contributions are licensed
+and agree by submitting the patch that your contributions are licensed
 under the [MIT license](https://raw.githubusercontent.com/aseprite/laf/main/LICENSE.txt)
 terms.
 
@@ -13,13 +13,13 @@ We have some rules for commits that are contributed:
 * Split your changes in the most atomic commits possible: one commit
   for feature, or fix.
 * Rebase your commits to the `main` branch (or `beta` if you are
-  targetting the beta version).
+  targeting the beta version).
 * Wrap your commit messages at 72 characters.
 * The first line of the commit message is the subject line.
 * Write the subject line in the imperative mood, e.g. "Fix something",
   not "Fixed something".
 * For platform-specific commits start the subject line using
   `[win]`, `[osx]`, or `[x11]` prefixes.
 * Check the spelling of your code, comments and commit messages.
-* We're using some C++17 features, targetting macOS 10.9 mainly as the
+* We're using some C++17 features, targeting macOS 10.9 mainly as the
   oldest platform (and the one limiting us to newer C++ standards).