fix(xpub-edit): spaces are being eaten on firefox

there is an outstanding issue on ProseMirror (https://github.com/ProseMirror/prosemirror/issues/651)
to prevent that a css property can be added ```

#430

packages/components/xpub-edit/src/components/withStyles.js

@@ -70,6 +70,7 @@ export const withEditorStyle = Component => styled(Component).attrs({
   &:focus .placeholder {
     display: none;
   }
+  white-space: pre-wrap;
 
   ${contentStyles};