Correct release_status for bigquery_storage (#6767)

Author: busunkim96

setup.py

@@ -22,7 +22,7 @@
 name = 'google-cloud-bigquery-storage'
 description = 'BigQuery Storage API API client library'
 version = '0.1.0'
-release_status = '3 - Alpha'
+release_status = 'Development Status :: 3 - Alpha'
 dependencies = [
     'google-api-core[grpc] >= 1.5.1, < 2.0.0dev',
     'enum34; python_version < "3.4"',