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

This reverts commit 09a8fec2

src/Lifecycle.js

@@ -524,7 +524,7 @@ export function logout() {
             console.log("Failed to call logout API: token will not be invalidated");
             onLoggedOut();
         },
-    ).then();
+    ).done();
 }
 
 export function softLogout() {
@@ -608,7 +608,7 @@ export function onLoggedOut() {
     // that can occur when components try to use a null client.
     dis.dispatch({action: 'on_logged_out'}, true);
     stopMatrixClient();
-    _clearStorage().then();
+    _clearStorage().done();
 }
 
 /**