Use the dev branching model for QtWebSockets

There seems to be some enforcement introduced lately about stop using master in
repositories for consistency.

Change-Id: I1e2a154f339e31ab7c129c83b133479b1060e3d1
Reviewed-by: Kurt Pattyn <pattyn.kurt@gmail.com>
Reviewed-by: Simo Fält <simo.falt@digia.com>