Bump firebaseui from 2.5.1 to 3.6.1

As explained in firebase/firebaseui-web#224, 
we'll continue to use the CDN install version until the NPM method has 
multi-language support

_includes/components/firebase/ui.liquid → _includes/components/firebase/ui.html

@@ -6,6 +6,8 @@
   {% assign firebase-lang = "es_419" %}
 {% endif %}
 
-<script src="https://www.gstatic.com/firebasejs/ui/2.5.1/firebase-ui-auth__{{ firebase-lang }}.js"></script>
-<script src="{{ '/assets/js/firebase/firebase-ui.js' | relative_url }}"></script>
-<link type="text/css" rel="stylesheet" href="https://www.gstatic.com/firebasejs/ui/2.5.1/firebase-ui-auth.css" />
+<link type="text/css" rel="stylesheet" href="https://www.gstatic.com/firebasejs/ui/3.6.1/firebase-ui-auth.css" />
+<script src="https://www.gstatic.com/firebasejs/ui/3.6.1/firebase-ui-auth__{{ firebase-lang }}.js"></script>
+<script type="text/javascript">
+  {% include components/firebase/ui.js %}
+</script>

assets/js/firebase/firebase-ui.js → _includes/components/firebase/ui.js

@@ -1,7 +1,7 @@
 // FirebaseUI config.
 var uiConfig = {
   callbacks: {
-    signInSuccess: function(currentUser, credential, redirectUrl) {
+    signInSuccessWithAuthResult: function(currentUser, credential, redirectUrl) {
       // Return type determines whether we continue the redirect automatically
       // or whether we leave that to developer to handle.
       return true;
@@ -19,7 +19,11 @@ var uiConfig = {
   // Comment the next line to activate CredentialHelper
   credentialHelper: firebaseui.auth.CredentialHelper.NONE,
   // Terms of service url can be specified and will show up in the widget.
-  tosUrl: '{{ site.amazon-s3 }}/assets/pdf/documents/terms-and-conditions.pdf'
+  tosUrl: '{{ site.amazon-s3 }}/assets/pdf/documents/terms-and-conditions.pdf',
+  // Privacy policy url/callback.
+  privacyPolicyUrl: function() {
+    window.location.assign('{{ site.amazon-s3 }}/assets/pdf/documents/privacy-notice.pdf');
+  }
 };
 
 // Initialize the FirebaseUI Widget using Firebase.