Add SimpleCov coverage set up for gRPC ruby
diff --git a/src/ruby/grpc.gemspec b/src/ruby/grpc.gemspec
index 12d4ab1..3e87a42 100755
--- a/src/ruby/grpc.gemspec
+++ b/src/ruby/grpc.gemspec
@@ -27,6 +27,7 @@
   s.add_dependency 'minitest', '~> 5.4'  # reqd for interop tests
   s.add_dependency 'xray', '~> 1.1'
 
+  s.add_development_dependency 'simplecov', '~> 0.9'
   s.add_development_dependency 'bundler', '~> 1.9'
   s.add_development_dependency 'rake', '~> 10.4'
   s.add_development_dependency 'rake-compiler', '~> 0.9'