Fixed typo in comment.

--HG--
extra : convert_revision : svn%3Afdd8eb12-d10e-0410-9acb-85c331704f74/trunk%404148

dlib/cmd_line_parser/cmd_line_parser_kernel_1.h

@@ -137,7 +137,7 @@ namespace dlib
                     name_                == name()
                     description_         == description()
                     number_of_arguments_ == number_of_arguments()
-                    options[index]       == operator[](index)
+                    options[N][arg]      == argument(arg,N)
                     num_present          == count()                    
             !*/