Support for Node v8 (TryGhost#9183)

no issue

- bump dependencies because of failing tests
- added package-lock.json to gitignore, because we use yarn
- run v8 on travis
- support v8 engine in package.json

.gitignore

@@ -12,6 +12,7 @@ b-cov
 pids
 results
 
+package-lock.json
 npm-debug.log
 node_modules
 bower_components

.travis.yml

@@ -1,6 +1,7 @@
 language: node_js
 # When changing node version also update it on lines 34, 36 and 46.
 node_js:
+  - "8"
   - "6"
   - "4"
 

package.json

@@ -24,7 +24,7 @@
     "init": "yarn global add knex-migrator ember-cli grunt-cli && yarn install && grunt symlink && grunt init || true"
   },
   "engines": {
-    "node": "^4.5.0 || ^6.9.0"
+    "node": "^4.5.0 || ^6.9.0 || ^8.8.0"
   },
   "dependencies": {
     "amperize": "0.3.5",
@@ -50,18 +50,18 @@
     "extract-zip-fork": "1.5.1",
     "fs-extra": "3.0.1",
     "ghost-gql": "0.0.8",
-    "ghost-ignition": "2.8.14",
+    "ghost-ignition": "2.8.16",
     "ghost-storage-base": "0.0.1",
     "glob": "5.0.15",
     "got": "7.1.0",
-    "gscan": "1.2.0",
+    "gscan": "1.2.1",
     "html-to-text": "3.3.0",
     "image-size": "0.6.1",
     "intl": "1.2.5",
     "intl-messageformat": "1.3.0",
     "jsonpath": "0.2.12",
     "knex": "0.12.9",
-    "knex-migrator": "2.1.8",
+    "knex-migrator": "2.1.9",
     "lodash": "4.17.4",
     "markdown-it": "8.4.0",
     "markdown-it-footnote": "3.0.1",