Use grpc:: counterparts in ruby code generator
diff --git a/src/compiler/ruby_generator_map-inl.h b/src/compiler/ruby_generator_map-inl.h
index f902b6d..6b87774 100644
--- a/src/compiler/ruby_generator_map-inl.h
+++ b/src/compiler/ruby_generator_map-inl.h
@@ -34,11 +34,12 @@
 #ifndef GRPC_INTERNAL_COMPILER_RUBY_GENERATOR_MAP_INL_H
 #define GRPC_INTERNAL_COMPILER_RUBY_GENERATOR_MAP_INL_H
 
+#include "src/compiler/config.h"
+
 #include <iostream>
 #include <initializer_list>
 #include <map>
 #include <ostream>  // NOLINT
-#include <string>
 #include <vector>
 
 using std::initializer_list;
@@ -49,18 +50,18 @@
 
 // Converts an initializer list of the form { key0, value0, key1, value1, ... }
 // into a map of key* to value*. Is merely a readability helper for later code.
-inline std::map<std::string, std::string> ListToDict(
-    const initializer_list<std::string> &values) {
+inline std::map<grpc::string, grpc::string> ListToDict(
+    const initializer_list<grpc::string> &values) {
   if (values.size() % 2 != 0) {
     std::cerr << "Not every 'key' has a value in `values`."
               << std::endl;
   }
-  std::map<std::string, std::string> value_map;
+  std::map<grpc::string, grpc::string> value_map;
   auto value_iter = values.begin();
   for (unsigned i = 0; i < values.size() / 2; ++i) {
-    std::string key = *value_iter;
+    grpc::string key = *value_iter;
     ++value_iter;
-    std::string value = *value_iter;
+    grpc::string value = *value_iter;
     value_map[key] = value;
     ++value_iter;
   }