fix(package): update @firebase/database to version 0.4.8

Closes #638

Author: greenkeeper[bot]

package.json

@@ -19,7 +19,7 @@
   "dependencies": {
     "@firebase/app": "^0.3.4",
     "@firebase/auth": "^0.7.7",
-    "@firebase/database": "^0.3.6",
+    "@firebase/database": "^0.4.8",
     "@firebase/messaging": "^0.3.6",
     "@firebase/storage": "^0.2.3",
     "@material-ui/core": "^3.1.1",