Changed print statement so the output is slightly less confusing.

--HG--
extra : convert_revision : svn%3Afdd8eb12-d10e-0410-9acb-85c331704f74/trunk%403774

dlib/optimization/optimization_stop_strategies.h

@@ -140,7 +140,7 @@ namespace dlib
             if (_verbose)
             {
                 using namespace std;
-                cout << "iteration: " << _cur_iter << "   objective: " << funct_value << "   derivative norm: " << length(funct_derivative) << endl;
+                cout << "iteration: " << _cur_iter << "   objective: " << funct_value << "   gradient norm: " << length(funct_derivative) << endl;
             }
 
             ++_cur_iter;