[WebSocket] Fix typo in an opening handshake fail message.

BUG=NONE
R=tyoshino@chromium.org

Review URL: https://codereview.chromium.org/93513004

git-svn-id: svn://svn.chromium.org/blink/trunk@163317 bbb929c8-8fbe-4397-9dbb-9b2b20218538