Restrict amber version as well.

bower.json

@@ -23,7 +23,7 @@
   ],
   "private": false,
   "dependencies": {
-    "amber": ">=0.18.0",
+    "amber": ">=0.18.0 <0.20.0",
     "jquery": ">=1.7.0"
   },
   "devDependencies": {