using argv[0] represent binary executable files' name in help() function

in sample codes instead of cpp files' name.

samples/cpp/convexhull.cpp

@@ -5,11 +5,11 @@
 using namespace cv;
 using namespace std;
 
-static void help()
+static void help(char** argv)
 {
     cout << "\nThis sample program demonstrates the use of the convexHull() function\n"
          << "Call:\n"
-         << "./convexhull\n" << endl;
+         << argv[0] << endl;
 }
 
 int main( int argc, char** argv )
@@ -17,7 +17,7 @@ int main( int argc, char** argv )
     CommandLineParser parser(argc, argv, "{help h||}");
     if (parser.has("help"))
     {
-        help();
+        help(argv);
         return 0;
     }
     Mat img(500, 500, CV_8UC3);