newline in documentation

Author: mhaseebtariq

doc/source/io.rst

@@ -4479,7 +4479,8 @@ Authentication via ``application default credentials`` is also possible. This is
 if the parameter ``private_key`` is not provided. This method also requires that
 the credentials can be fetched from the environment the code is running in.
 Otherwise, the OAuth2 client-side authentication is used.
-Additional information on `application default credentials <https://developers.google.com/identity/protocols/application-default-credentials>`__.
+Additional information on
+`application default credentials <https://developers.google.com/identity/protocols/application-default-credentials>`__.
 
 .. versionadded:: 0.19.0