try to see if this fixes safari back

on of the 2 changes (updating dom async from compositionend,
or ignoring keydown while composing) here has, while fixing chrome,
broken safari.

Don't do the async dom updating for safari if that was it.

src/components/views/rooms/EditMessageComposer.js

@@ -127,6 +127,7 @@ export default class EditMessageComposer extends React.Component {
     }
 
     _onKeyDown = (event) => {
+        // ignore any keypress while doing IME compositions
         if (this._editorRef.isComposing(event)) {
             return;
         }