Fix syntax highlighting missing a closing tag (#911)

SUPERCILEX · samtstern · commit 9dc4c120f33d · 2017-09-15T08:59:24.000-07:00
diff --git a/auth/README.md b/auth/README.md
@@ -417,6 +417,7 @@ Second, ensure the three standard AppCompat color resources are defined with you
     <item name="colorPrimaryDark">@color/colorPrimaryDark</item>
     <item name="colorAccent">@color/colorAccent</item>
 </style>
+```
 
 If you would like more control over FirebaseUI's styling, you can define your own custom style
 to override certain or all styling attributes. For example, a green sign-in theme:
