change grpc_tools_node_protoc_plugin binary name to protoc-gen-js-grpc

[otaxhu]

Is your feature request related to a problem? Please describe.

Compatibility issues with already existing protoc, I needed to make a symbolic link from grpc_tools_node_protoc_plugin to protoc-gen-js-grpc so I can execute succesfully the command:

$ protoc --js-grpc_out=directory/

The java, c#, ruby, python and golang plugins has this behaviour, all of the plugins called protoc-gen-<lang-name>-grpc and being succesfully invoked from protoc and generating its respective classes and methods.