Update ruby google-protobuf dependency to 3.0
diff --git a/grpc.gemspec b/grpc.gemspec
index 369851b..00113cb 100755
--- a/grpc.gemspec
+++ b/grpc.gemspec
@@ -27,7 +27,7 @@
   s.require_paths = %w( src/ruby/bin src/ruby/lib src/ruby/pb )
   s.platform      = Gem::Platform::RUBY
 
-  s.add_dependency 'google-protobuf', '~> 3.0.0.alpha.5.0.3'
+  s.add_dependency 'google-protobuf', '~> 3.0'
   s.add_dependency 'googleauth',      '~> 0.5.1'
 
   s.add_development_dependency 'bundler',            '~> 1.9'