fix(package): update @firebase/app-types to version 0.6.1

Closes #23

Author: greenkeeper[bot]

package.json

@@ -5,7 +5,7 @@
   "private": true,
   "license": "MIT",
   "dependencies": {
-    "@firebase/app-types": "0.5.1",
+    "@firebase/app-types": "0.6.1",
     "@types/bootstrap": "4.3.1",
     "@types/jquery": "3.2.17",
     "@types/mustache": "4.0.0",