Small fix to error text
Small fix to error text

Change-Id: Ie46b5ad5892e55a20ba00bdf659d2395c40f95c3
Reviewed-by: Kurt Pattyn <da83d6ada5df79ff647b4271d0d788c6f1bafca2@gmail.com>

remimixlr/QtWebsocket,pixty/qtwebsockets,SfietKonstantin/qtwebsockets,pixty/qtwebsockets