docs: update github repo url (#88)

Author: dandhlee

setup.py

@@ -31,7 +31,7 @@
  author="Google LLC",
  author_email="googleapis-packages@google.com",
  license="Apache 2.0",
- url="https://github.com/googleapis/python-google-cloud-video-stitcher",
+ url="https://github.com/googleapis/python-video-stitcher",
  version=version,
  long_description=readme,
  packages=setuptools.PEP420PackageFinder.find(),