Merge pull request inversify#47 from inversify/greenkeeper/gulp-typescript-4.0.0

Update gulp-typescript to the latest version 🚀

Author: remojansen

package.json

@@ -32,7 +32,7 @@
   "devDependencies": {
     "gulp": "3.9.1",
     "gulp-tslint": "8.1.2",
-    "gulp-typescript": "4.0.0-alpha.2",
+    "gulp-typescript": "4.0.0",
     "run-sequence": "2.2.1",
     "typescript": "2.6.2",
     "tslint": "5.9.1"