fix(c++): use std::move to reduce copy (#859)

Author: SYaoJun

cpp/src/graphar/types.h

@@ -286,7 +286,7 @@ inline std::vector<std::string> SplitString(const std::string& str,
   std::string token;
   std::istringstream tokenStream(str);
   while (std::getline(tokenStream, token, delimiter)) {
-    tokens.push_back(token);
+    tokens.push_back(std::move(token));
   }
   return tokens;
 }

cpp/src/graphar/version_parser.cc

@@ -21,6 +21,7 @@
 #include <iostream>
 #include <regex>  // NOLINT
 #include <string>
+#include <utility>
 
 #include "graphar/version_parser.h"
 
@@ -92,7 +93,7 @@ std::vector<std::string> parseUserDefineTypesImpl(
       std::string type = types_str.substr(pos, next_pos - pos);
       trim(type);
       if (!type.empty()) {
-        user_define_types.push_back(type);
+        user_define_types.push_back(std::move(type));
       }
       if (next_pos != std::string::npos) {
         pos = next_pos + 1;