Merge pull request #5858 from Kiran-Rao/addUserToDefaultChannels

addUserToDefaultChannels let to const

packages/rocketchat-lib/server/functions/addUserToDefaultChannels.js

 RocketChat.addUserToDefaultChannels = function(user, silenced) {
 	RocketChat.callbacks.run('beforeJoinDefaultChannels', user);
-	let defaultRooms = RocketChat.models.Rooms.findByDefaultAndTypes(true, ['c', 'p'], {fields: {usernames: 0}}).fetch();
+	const defaultRooms = RocketChat.models.Rooms.findByDefaultAndTypes(true, ['c', 'p'], {fields: {usernames: 0}}).fetch();
 	defaultRooms.forEach((room) => {
 
 		// put user in default rooms
-		let muted = room.ro && !RocketChat.authz.hasPermission(user._id, 'post-readonly');
+		const muted = room.ro && !RocketChat.authz.hasPermission(user._id, 'post-readonly');
 		RocketChat.models.Rooms.addUsernameById(room._id, user.username, muted);
 
 		if (!RocketChat.models.Subscriptions.findOneByRoomIdAndUserId(room._id, user._id)) {