 Pin the protoc-docs-plugin to version 0.2.0 (#297)
 Pin the protoc-docs-plugin to version 0.2.0 (#297)

Pin the protoc-docs-plugin to version 0.2.0 which contains a critical fix related to proto3 nested message.

googleapis/artman,googleapis/artman,ethanbao/artman,googleapis/artman,ethanbao/artman