Update pins of 'googleapis-common-protos. (#8688)

Toward #8686.

Author: tseaver

setup.py

@@ -29,7 +29,7 @@
 # 'Development Status :: 5 - Production/Stable'
 release_status = "Development Status :: 5 - Production/Stable"
 dependencies = [
-    "googleapis-common-protos >= 1.5.3, != 1.5.4, < 2.0dev",
+    "googleapis-common-protos >= 1.6.0, < 2.0dev",
     "protobuf >= 3.4.0",
     "google-auth >= 0.4.0, < 2.0dev",
     "requests >= 2.18.0, < 3.0.0dev",