Remove `author` field from pubspec.yaml (#323)

It is no longer in use
diff --git a/protoc_plugin/pubspec.yaml b/protoc_plugin/pubspec.yaml
index 3bdd1cb..3e71302 100644
--- a/protoc_plugin/pubspec.yaml
+++ b/protoc_plugin/pubspec.yaml
@@ -1,6 +1,5 @@
 name: protoc_plugin
 version: 19.0.2
-author: Dart Team <misc@dartlang.org>
 description: Protoc compiler plugin to generate Dart code
 homepage: https://github.com/dart-lang/protobuf