Bump grpcio from 1.30.0 to 1.53.0 in /plugins/pubsub

Bumps [grpcio](https://github.com/grpc/grpc) from 1.30.0 to 1.53.0.
- [Release notes](https://github.com/grpc/grpc/releases)
- [Changelog](https://github.com/grpc/grpc/blob/master/doc/grpc_release_schedule.md)
- [Commits](https://github.com/grpc/grpc/compare/v1.30.0...v1.53.0)

---
updated-dependencies:
- dependency-name: grpcio
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

plugins/pubsub/setup.py

@@ -15,7 +15,7 @@ setup(
     install_requires=[
         'google-cloud-pubsub',
         'oauth2client',
-        'grpcio==1.30.0'
+        'grpcio==1.53.0'
     ],
     include_package_data=True,
     zip_safe=True,