fix(package): update firebase to version 5.0.4

Closes #6

Author: greenkeeper[bot]

package.json

@@ -9,7 +9,7 @@
     "@polymer/iron-icons": "^3.0.0-pre.12",
     "@polymer/paper-button": "^3.0.0-pre.12",
     "@polymer/paper-item": "^3.0.0-pre.12",
-    "firebase": "^4.12.1",
+    "firebase": "^5.0.4",
     "fit-html": "^0.5.4",
     "qs": "^6.5.1",
     "redux-devtools-extension": "^2.13.2",