Update bower.json

Following the discussions at mendhak#95 (comment)

Author: canercandan

bower.json

@@ -12,7 +12,7 @@
     "assets"
   ],
   "dependencies": {
-    "angular": "~1.4.0",
+    "angular": "^1.4.0",
     "intro.js": "~2.3.0"
   },
   "devDependencies": {}