cli: fix FPS display

1) the float format displayed like 50.123456789123456 wouldn't fit
   into the window title bar, and
2) most likely not into the char buffer of length 20, of which half
   was already used for the desmume string.

desmume/src/frontend/posix/cli/main.cpp

@@ -582,7 +582,7 @@ int main(int argc, char ** argv) {
       fps_frame_counter = 0;
       fps_timing = 0;
 
-      snprintf( win_title, sizeof(win_title), "Desmume %f", fps);
+      snprintf( win_title, sizeof(win_title), "Desmume %.02f", fps);
 
       SDL_SetWindowTitle( window, win_title );
     }