chore: reference main branch of google-cloud-python (#191)

Co-authored-by: Anthonios Partheniou <[email protected]>

packages/google-cloud-language/README.rst

@@ -17,7 +17,7 @@ with your document storage on Google Cloud Storage.
 - `Product Documentation`_
 
 .. |GA| image:: https://img.shields.io/badge/support-GA-gold.svg
-   :target: https://github.com/googleapis/google-cloud-python/blob/master/README.rst#general-availability
+   :target: https://github.com/googleapis/google-cloud-python/blob/main/README.rst#general-availability
 .. |pypi| image:: https://img.shields.io/pypi/v/google-cloud-language.svg
    :target: https://pypi.org/project/google-cloud-language/
 .. |versions| image:: https://img.shields.io/pypi/pyversions/google-cloud-language.svg