Fix React crash when using a non-default homeserver on soft logout

The function used exists on the peg, not the client. This commit also fixes the name of the function in a backwards compatible way.

src/components/structures/auth/SoftLogout.js

@@ -37,7 +37,7 @@ export default class SoftLogout extends React.Component {
         const hsUrl = MatrixClientPeg.get().getHomeserverUrl();
         const domainName = hsUrl === defaultServerConfig.hsUrl
             ? defaultServerConfig.hsName
-            : MatrixClientPeg.get().getHomeServerName();
+            : MatrixClientPeg.getHomeserverName();
 
         const userId = MatrixClientPeg.get().getUserId();
         const user = MatrixClientPeg.get().getUser(userId);