Update third_party.md

Add GDScript Protobuf implementation

docs/third_party.md

diff --git a/docs/third_party.md b/docs/third_party.md
index 1b03b9f..fa21462 100644
--- a/docs/third_party.md
+++ b/docs/third_party.md
@@ -39,6 +39,7 @@
 * Erlang: https://code.google.com/p/protoc-gen-erl/
 * Erlang: https://github.com/basho/erlang_protobuffs
 * Erlang: https://github.com/tomas-abrahamsson/gpb
+* GDScript: https://github.com/oniksan/godobuf (Godot v3 engine plugin)
 * Go: https://github.com/golang/protobuf (Google-official implementation)
 * Go: https://github.com/akunspy/gopbuf
 * Go: https://github.com/gogo/protobuf