package/webkitgtk: security bump to version 2.26.4

package/webkitgtk: security bump to version 2.26.4

Fixes the following security issues:

- CVE-2020-3862: Impact: A malicious website may be able to cause a denial
  of service.  Description: A denial of service issue was addressed with
  improved memory handling.

- CVE-2020-3864: Impact: A DOM object context may not have had a unique
  security origin.  Description: A logic issue was addressed with improved
  validation.

- CVE-2020-3865: Impact: A top-level DOM object context may have incorrectly
  been considered secure.  Description: A logic issue was addressed with
  improved validation.

- CVE-2020-3867: Impact: Processing maliciously crafted web content may lead
  to universal cross site scripting.  Description: A logic issue was
  addressed with improved state management.

- CVE-2020-3868: Impact: Processing maliciously crafted web content may lead
  to arbitrary code execution.  Description: Multiple memory corruption
  issues were addressed with improved memory handling.

For more details, see the advisory:
https://webkitgtk.org/security/WSA-2020-0002.html

While we are at it, adjust the white space in the .hash function to match
the new agreements.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>