Fixed typo on the two emails example

Author: Javierieh

reference/forms/types/collection.rst

@@ -113,7 +113,7 @@ your form):
 
 .. code-block:: html
 
-    <input type="email" id="form_emails_1" name="form[emails][0]" value="foo@foo.com" />
+    <input type="email" id="form_emails_0" name="form[emails][0]" value="foo@foo.com" />
     <input type="email" id="form_emails_1" name="form[emails][1]" value="bar@bar.com" />
 
 To allow your user to add another email, just set `allow_add`_ to ``true``