Merge pull request #306 from Liuchang0812/fix_cast

Update logging.cc

util/logging.cc

@@ -45,7 +45,7 @@ int AppendHumanBytes(uint64_t bytes, char* output, int len) {
 
 void AppendNumberTo(std::string* str, uint64_t num) {
   char buf[30];
-  snprintf(buf, sizeof(buf), "%llu", (unsigned long long) num);
+  snprintf(buf, sizeof(buf), "%" PRIu64, num);
   str->append(buf);
 }