fix(package): update firebase to version 4.12.1

Closes #4

Author: greenkeeper[bot]

package.json

@@ -26,7 +26,7 @@
     "es6-promise": "^4.1.1",
     "express": "^4.16.2",
     "extract-text-webpack-plugin": "^3.0.2",
-    "firebase": "4.10.0",
+    "firebase": "4.12.1",
     "lru-cache": "^4.1.1",
     "route-cache": "0.4.4",
     "serve-favicon": "^2.4.5",