Update contents/stacks_and_queues/code/c++/queue.cpp

adding version T const& front() const

Co-authored-by: Dimitri Belopopsky <[email protected]>

Author: ishwar00

contents/stacks_and_queues/code/c++/queue.cpp

@@ -57,6 +57,7 @@ namespace my {
         }
 
         T& front() const { return _front->value; }
+        T const& front() const { return _front->value; }
         // returning reference can very usefull if someone wants to modify _front element
 
         size_t size() const { return count; }