bump version to 4.4.0 in README.md (#669)

Author: n0mer

README.md

@@ -195,8 +195,8 @@ for a more in-depth example, showcasing a Single Page Application mode.
        * TODO(DEVELOPER): Paste the initialization snippet from:
        * Firebase Console > Overview > Add Firebase to your web app. *
        ***************************************************************************************** -->
-    <script src="https://www.gstatic.com/firebasejs/ui/4.3.0/firebase-ui-auth.js"></script>
-    <link type="text/css" rel="stylesheet" href="https://www.gstatic.com/firebasejs/ui/4.3.0/firebase-ui-auth.css" />
+    <script src="https://www.gstatic.com/firebasejs/ui/4.4.0/firebase-ui-auth.js"></script>
+    <link type="text/css" rel="stylesheet" href="https://www.gstatic.com/firebasejs/ui/4.4.0/firebase-ui-auth.css" />
     <script type="text/javascript">
       // FirebaseUI config.
       var uiConfig = {