CZString assignment operator - pass by reference

The assignment operator of CZString is not passed by reference. It is reported as issue in static analyser tool.

Author: ya1gaurav

src/lib_json/json_value.cpp

@@ -247,7 +247,7 @@ void Value::CZString::swap(CZString& other) {
   std::swap(index_, other.index_);
 }
 
-Value::CZString& Value::CZString::operator=(CZString other) {
+Value::CZString& Value::CZString::operator=(CZString& other) {
   swap(other);
   return *this;
 }