fix missing format argument

src/main.cpp

@@ -58,7 +58,7 @@ int main( int argc, char **argv )
       {
         if(strcmp(argv[i]+1,"help")!=0 && strcmp(argv[i]+1,"-help")!=0)
           printf( "Unknown parameter.\n\n" );
-        printf(help);
+        printf("%s", help);
         exit(-2);
       }
     }