docs: Update the documentation link for GoogleCredential from deprecated version to newer version (#1652)
docs: Update the documentation link for GoogleCredential from deprecated version to newer version (#1652)

* Updated the link to GoogleCredential

* Changed the documentation to GoogleCredential to newer version

* Removed typos from oauth-2.0.md
googleapis/google-api-java-client,googleapis/google-api-java-client,googleapis/google-api-java-client,googleapis/google-api-java-client