Change version to 1.39.0 (grpc#4541)

[skip ci] Skipping Travis. Version number change only

Co-authored-by: Zach Reyes <[email protected]>

Change version to 1.38.1 (grpc#4573)

Change version to 1.40.0-dev (grpc#4543)

Change version to 1.38.0 (grpc#4418)

Change version to 1.39.0-dev (grpc#4420)

Change version to 1.37.1 (grpc#4415)

Change version to 1.37.0 (grpc#4304)

Change version to 1.38.0-dev (grpc#4306)

Change version to 1.36.1 (grpc#4297)

Change version to 1.35.1 (grpc#4260)