PLT-3473 Made shortcuts only work for CMD on OSX (#3479)

* checked for CMD key

* changed method of checking

webapp/components/file_upload.jsx

@@ -280,7 +280,7 @@ class FileUpload extends React.Component {
     }
 
     keyUpload(e) {
-        if ((e.ctrlKey || e.metaKey) && e.keyCode === Constants.KeyCodes.U) {
+        if (Utils.cmdOrCtrlPressed(e) && e.keyCode === Constants.KeyCodes.U) {
             e.preventDefault();
             if (this.props.postType === 'post' && document.activeElement.id === 'post_textbox' || this.props.postType === 'comment' && document.activeElement.id === 'reply_textbox') {
                 $(this.refs.fileInput).focus().trigger('click');