Restrict amber version as well.

bower.json

@@ -26,7 +26,7 @@
   ],
   "private": false,
   "dependencies": {
-    "amber": ">=0.15.0",
+    "amber": ">=0.15.0 <0.20.0",
     "domite": "^0.4.0 || ^0.5.0 || ^0.6.0"
   },
   "devDependencies": {