Bump amber dep to >=0.21.0.

B/c: uses `global`.

bower.json

@@ -18,7 +18,7 @@
     "MIT"
   ],
   "dependencies": {
-    "amber": ">0.19.1",
+    "amber": ">=0.21.0",
     "amber-contrib-web": ">=0.5.0",
     "jquery-ui": ">=1.9.2",
     "bootstrap": "^3.3.4",