Update link to protoc-plugin (#188)

diff --git a/protobuf/README.md b/protobuf/README.md
index 13644f3..1119338 100644
--- a/protobuf/README.md
+++ b/protobuf/README.md
@@ -14,4 +14,4 @@
 * [Dart generated code guide](https://developers.google.com/protocol-buffers/docs/reference/dart-generated)
 * [Dart API](https://pub.dartlang.org/documentation/protobuf/latest/)
 * [Protobuf repository](https://github.com/google/protobuf)
-* [Protoc plugin project](https://github.com/dart-lang/dart-protoc-plugin)
+* [Protoc plugin project](https://github.com/dart-lang/protobuf/tree/master/protoc_plugin)