attempt to fix clash of Cmd-M on Mac. Should fix vector-im/riot-web#7047

Signed-off-by: Michael Telatynski <7t3chguy@gmail.com>

src/components/views/rooms/MessageComposerInput.js

@@ -734,6 +734,7 @@ export default class MessageComposerInput extends React.Component {
             }[ev.keyCode];
 
             if (ctrlCmdCommand) {
+                ev.preventDefault(); // to prevent clashing with Mac's minimize window
                 return this.handleKeyCommand(ctrlCmdCommand);
             }
         }