Bumped major test dependencies (#10403)

refs #9389

- eslint@5.12.1, eslint-plugin-ghost@0.1.0, grunt-contrib-clean@2.0.0, grunt-contrib-uglify@4.0.0, grunt-eslint@21.0.0, grunt-mocha-cli@4.0.0, grunt-shell@3.0.1, mocha@5.2
.0, nock@10.0.6, rewire@4.0.1

All of them dropped Node v4. I was not able to find any other big breaking changes, which affect us right now.

core/server/lib/common/i18n.js

@@ -17,15 +17,15 @@ const supportedLocales = ['en'],
     settingsCache = require('../../services/settings/cache'),
     _private = {};
 
-    // currentLocale, dynamically based on overall settings (key = "default_locale") in the settings db table
-    // (during Ghost's initialization, settings available inside i18n functions below; see core/server/index.js)
-    //
-    // E.g.: en = English (default), es = Spanish, en-US = American English, etc.
-    // Standard:
-    // Language tags in HTML and XML
-    // https://www.w3.org/International/articles/language-tags/
-    //
-    // The corresponding translation files should be at content/themes/mytheme/locales/es.json, etc.
+// currentLocale, dynamically based on overall settings (key = "default_locale") in the settings db table
+// (during Ghost's initialization, settings available inside i18n functions below; see core/server/index.js)
+//
+// E.g.: en = English (default), es = Spanish, en-US = American English, etc.
+// Standard:
+// Language tags in HTML and XML
+// https://www.w3.org/International/articles/language-tags/
+//
+// The corresponding translation files should be at content/themes/mytheme/locales/es.json, etc.
 let currentLocale,
     activeTheme,
     coreStrings,

package.json

@@ -111,34 +111,34 @@
     "sqlite3": "4.0.6"
   },
   "devDependencies": {
-    "eslint": "4.19.1",
-    "eslint-plugin-ghost": "0.0.27",
+    "eslint": "5.12.1",
+    "eslint-plugin-ghost": "0.1.0",
     "grunt": "1.0.3",
     "grunt-bg-shell": "2.3.3",
     "grunt-cli": "1.3.2",
-    "grunt-contrib-clean": "1.1.0",
+    "grunt-contrib-clean": "2.0.0",
     "grunt-contrib-compress": "1.4.3",
     "grunt-contrib-copy": "1.0.0",
     "grunt-contrib-symlink": "^1.0.0",
-    "grunt-contrib-uglify": "3.3.0",
+    "grunt-contrib-uglify": "4.0.0",
     "grunt-contrib-watch": "1.1.0",
     "grunt-cssnano": "2.1.0",
     "grunt-docker": "0.0.11",
-    "grunt-eslint": "20.1.0",
+    "grunt-eslint": "21.0.0",
     "grunt-express-server": "0.5.4",
-    "grunt-mocha-cli": "3.0.0",
+    "grunt-mocha-cli": "4.0.0",
     "grunt-mocha-istanbul": "5.0.2",
-    "grunt-shell": "2.1.0",
+    "grunt-shell": "3.0.1",
     "grunt-subgrunt": "1.3.0",
     "grunt-update-submodules": "0.4.1",
     "istanbul": "0.4.5",
     "matchdep": "2.0.0",
     "minimist": "1.2.0",
-    "mocha": "4.1.0",
+    "mocha": "5.2.0",
     "mock-knex": "0.4.3",
-    "nock": "9.4.0",
+    "nock": "10.0.6",
     "proxyquire": "2.1.0",
-    "rewire": "3.0.2",
+    "rewire": "4.0.1",
     "should": "13.2.3",
     "should-http": "0.1.1",
     "sinon": "7.2.3",