Reject test directory in src/ruby/pb from packing as gem

This seems to be a test directory, as the name implies.
So This directory does not need to be include as grpc gem.
diff --git a/templates/grpc.gemspec.template b/templates/grpc.gemspec.template
index fb54de1..9945456 100644
--- a/templates/grpc.gemspec.template
+++ b/templates/grpc.gemspec.template
@@ -22,7 +22,9 @@
     s.files += Dir.glob('src/ruby/bin/**/*')
     s.files += Dir.glob('src/ruby/ext/**/*')
     s.files += Dir.glob('src/ruby/lib/**/*')
-    s.files += Dir.glob('src/ruby/pb/**/*')
+    s.files += Dir.glob('src/ruby/pb/**/*').reject do |f|
+      f.match(%r{^src/ruby/pb/test})
+    end
     s.files += Dir.glob('include/grpc/**/*')
     s.test_files = Dir.glob('src/ruby/spec/**/*')
     s.bindir = 'src/ruby/bin'