Revert "s/.done(/.then(/ since modern es6 track unhandled promise exceptions"

This reverts commit 09a8fec2

src/components/views/messages/MImageBody.js

@@ -289,7 +289,7 @@ export default class MImageBody extends React.Component {
                 this.setState({
                     error: err,
                 });
-            }).then();
+            }).done();
         }
 
         // Remember that the user wanted to show this particular image