feat(ios, sdk): bump firebase-ios-sdk from 7.5.0 to 7.6.0

https://firebase.google.com/support/release-notes/ios#7.6.0

Author: mikehardy

packages/app/package.json

@@ -62,7 +62,7 @@
   },
   "sdkVersions": {
     "ios": {
-      "firebase": "~> 7.5.0"
+      "firebase": "~> 7.6.0"
     },
     "android": {
       "minSdk": 16,