bump version to 0.3.7
bump version to 0.3.7

google/protobuf.dart,google/protobuf.dart,dart-lang/protobuf,dart-lang/dart-protobuf,google/protobuf.dart,dart-lang/protobuf,dart-lang/protobuf,taisph/dart-protoc-plugin,taisph/dart-protoc-plugin,taisph/dart-protoc-plugin,dart-lang/dart-protobuf,dart-lang/dart-protobuf