Restrict amber version as well.

bower.json

@@ -18,7 +18,7 @@
     "MIT"
   ],
   "dependencies": {
-    "amber": ">0.18.1",
+    "amber": ">0.18.1 <0.20.0",
     "amber-contrib-web": ">=0.4.0 <0.5.0",
     "jquery-ui": ">=1.9.2",
     "bootstrap": "^3.3.4",