package/webkitgtk: bump to version 2.22.4

This is a maintenance release of the current stable WebKitGTK+ version,
which contains security fixes for  CVE-2018-4345, CVE-2018-4372,
CVE-2018-4373, CVE-2018-4375, CVE-2018-4376, CVE-2018-4378,
CVE-2018-4382, CVE-2018-4386, CVE-2018-4392, and CVE-2018-4416.
Additionally, it fixes a few build failures, and a crash when using
certain version of Cairo.

Release notes can be found in the announcement:

  https://webkitgtk.org/2018/11/21/webkitgtk2.22.4-released.html

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

  https://webkitgtk.org/security/WSA-2018-0008.html



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