trim slashes from Site_Url - closes #2462

packages/rocketchat-livechat/client/views/app/livechatInstallation.js

 Template.livechatInstallation.helpers({
 	script () {
+		let siteUrl = s.rtrim(RocketChat.settings.get('Site_Url'), '/');
+
 		return `<!-- Start of Rocket.Chat Livechat Script -->
 <script type="text/javascript">
 (function(w, d, s, f, u) {
@@ -8,10 +10,10 @@ Template.livechatInstallation.helpers({
 	var h = d.getElementsByTagName(s)[0],
 		j = d.createElement(s);
 	j.async = true;
-	j.src = '${RocketChat.settings.get('Site_Url')}/packages/rocketchat_livechat/assets/rocket-livechat.js';
+	j.src = '${siteUrl}/packages/rocketchat_livechat/assets/rocket-livechat.js';
 	h.parentNode.insertBefore(j, h);
 })(window, document, 'script', 'initRocket', '${RocketChat.settings.get('Site_Url')}/livechat');
 </script>
 <!-- End of Rocket.Chat Livechat Script -->`;
 	}
-})
+});