Change the url to the canonical one (#6843)

Author: brianquinlan

setup.py

@@ -64,7 +64,7 @@
     author='Google LLC',
     author_email='[email protected]',
     license='Apache 2.0',
-    url='https://github.com/GoogleCloudPlatform/google-cloud-python',
+    url='https://github.com/googleapis/google-cloud-python',
     classifiers=[
         release_status,
         'Intended Audience :: Developers',