package/webkitgtk: security bump to version 2.22.6

package/webkitgtk: security bump to version 2.22.6

This is a maintenance release of the current stable WebKitGTK+ version,
which contains security fixes for CVE identifiers: CVE-2019-6212,
CVE-2019-6215, CVE-2019-6216, CVE-2019-6217, CVE-2019-6226,
CVE-2019-6227, CVE-2019-6229, CVE-2019-6233, and CVE-2019-6234.
Additionally, it contains a few minor fixes.

Release notes can be found in the announcement:

  https://webkitgtk.org/2019/02/09/webkitgtk2.22.6-released.html

More details on the issues covered by securit fixes can be found
in the corresponding security advisory:

  https://webkitgtk.org/security/WSA-2019-0001.html

Signed-off-by: Adrian Perez de Castro <aperez@igalia.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>