Restrict amber version as well.

bower.json

@@ -26,7 +26,7 @@
   ],
   "private": false,
   "dependencies": {
-    "amber": ">0.18.2"
+    "amber": ">0.18.2 <0.20.0"
   },
   "devDependencies": {
     "amber-contrib-legacy": ">=0.3.0 <0.5.0",