Add Elixir protobuf and gRPC to 3rd party doc

docs/third_party.md

@@ -32,6 +32,7 @@ These are projects we know about implementing Protocol Buffers for other program
 * Delphi: http://sourceforge.net/projects/protobuf-delphi/
 * Delphi: http://fundementals.sourceforge.net/dl.html
 * Elixir: https://github.com/jeremyong/exprotoc
+* Elixir: https://github.com/tony612/protobuf-elixir
 * Elm: https://github.com/tiziano88/elm-protobuf
 * Erlang: http://github.com/ngerakines/erlang_protobuffs/tree/master
 * Erlang: http://piqi.org/
@@ -117,6 +118,7 @@ GRPC (http://www.grpc.io/) is Google's RPC implementation for Protocol Buffers.
 * https://github.com/w359405949/libmaid (C++, Python)
 * https://github.com/madwyn/libpbrpc (C++)
 * https://github.com/SeriousMa/grpc-protobuf-validation (Java)
+* https://github.com/tony612/grpc-elixir (Elixir)
 
 ## Other Utilities