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

This reverts commit 09a8fec2

src/components/views/messages/MAudioBody.js

@@ -55,7 +55,7 @@ export default class MAudioBody extends React.Component {
             decryptFile(content.file).then(function(blob) {
                 decryptedBlob = blob;
                 return URL.createObjectURL(decryptedBlob);
-            }).then((url) => {
+            }).done((url) => {
                 this.setState({
                     decryptedUrl: url,
                     decryptedBlob: decryptedBlob,

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

src/components/views/messages/MVideoBody.js

@@ -115,7 +115,7 @@ module.exports = createReactClass({
                 this.setState({
                     error: err,
                 });
-            }).then();
+            }).done();
         }
     },