MOBILE-121: Gitignore EAS credentials in example app (#59)

credentials.json (and the credentials/ dir with the .p12 / provisioning
profile) must never be committed; only credentials/google-services.json
was ignored before. The leaked cert password is rotated separately.

Author: justSmK

.gitignore

@@ -25,7 +25,8 @@ yarn-error.log*
 # Credentials
 google-services.json
 GoogleService-Info.plist
-examples/MindboxExpoExample/credentials/google-services.json
+examples/MindboxExpoExample/credentials.json
+examples/MindboxExpoExample/credentials/
 
 # Misc
 .env