fix(package): update @firebase/storage to version 0.3.1

Closes #642

Author: greenkeeper[bot]

package.json

@@ -21,7 +21,7 @@
     "@firebase/auth": "^0.7.7",
     "@firebase/database": "^0.3.6",
     "@firebase/messaging": "^0.3.6",
-    "@firebase/storage": "^0.2.3",
+    "@firebase/storage": "^0.3.1",
     "@material-ui/core": "^3.1.1",
     "@material-ui/icons": "^3.0.1",
     "codemirror": "^5.40.2",