Added keycode Enter support for login

public/login/index.php

@@ -83,7 +83,8 @@ if ($function === 'oauth') {
 		<h4><?php l('login.login_with_mastodon', 'Log In using Mastodon') ?></h4>
 		<div class="columns">
 			<label for="instanceURL"><?php l('login.select_instance', 'Select your instance') ?></label>
-			<input class="u-full-width" type="text" placeholder="example.org" id="instanceURL" />
+			<input class="u-full-width" type="text" placeholder="example.org" id="instanceURL"
+				onkeypress="if (event.keyCode == 13) API.mastodon.registerInstance(null)"/>
 			<div class="right">
 				<input onclick="API.mastodon.registerInstance(null)" class="button-primary u-full-width bg-mastodon"
 					type="submit" value="<?php l('all.continue', 'Continue') ?> &gt;&gt;" />