imap: fix permFlags check after flag case normalization change

lib/imap.js

@@ -1343,7 +1343,7 @@ ImapConnection.prototype._move = function(which, uids, boxTo, cb) {
   var self = this;
   if (this._state.status !== STATES.BOXSELECTED)
     throw new Error('No mailbox is currently selected');
-  if (this._state.box.permFlags.indexOf('Deleted') === -1) {
+  if (this._state.box.permFlags.indexOf('deleted') === -1) {
     throw new Error('Cannot move message: '
                     + 'server does not allow deletion of messages');
   } else {