Upgrade JSC version

[Kudo]

Issue Description

Just seen https://webkitgtk.org/security/WSA-2018-0009.html that current WebKitGTK+ version has vulnerability issues.
However, the CVEs are kept secretly right now, I am not sure if these vulnerabilities are in JSC or maybe just in WebCore.
Do you have plans to upgrade WebKitGTK+ to 2.22.6?