Bump package versions

package.json

 {
   "private": true,
   "devDependencies": {
-    "gulp": "^3.8.8"
+    "gulp": "^3.9.1"
   },
   "dependencies": {
-    "laravel-elixir": "^4.0.0",
+    "laravel-elixir": "^5.0.0",
     "bootstrap-sass": "^3.0.0"
   }
 }