Change version to 1.29.1

examples: add go.mod to make examples a separate module (grpc#3546)

Change version to 1.29.0 (grpc#3509)

[skip ci] Skipping Travis. Version number change only

Change version to 1.30.0-dev (grpc#3511)

Change version to 1.28.1

Change version to 1.28.0 (grpc#3426)

[skip ci] Skipping Travis. Version number change only

Change version to 1.29.0-dev (grpc#3428)

Change version to 1.27.1

Change version to 1.28.0-dev (grpc#3342)

Change version to 1.27.0 (grpc#3340)

[skip ci] Skipping Travis. Version number change only