Await validPassword

validPassword [returns a promise](https://github.com/clintonwoo/hackernews-react-graphql/blob/master/src/data/models/User.js#L36-L40) which must therefore be `await`ed

Author: ecwyne

src/server.js

@@ -51,7 +51,7 @@ app.prepare()
         if (!user) {
           return done(null, false, { message: 'Incorrect username.' });
         }
-        if (!User.validPassword(username, password)) {
+        if (!(await User.validPassword(username, password))) {
           return done(null, false, { message: 'Incorrect password.' });
         }
         return done(null, user);