Security update for webkit2gtk3 (important)

This update for webkit2gtk3 fixes the following issues:

Update to version 2.18.5:

 + Disable SharedArrayBuffers from Web API.
 + Reduce the precision of "high" resolution time to 1ms.
 + bsc#1075419 - Security fixes: includes improvements to mitigate the
   effects of Spectre and Meltdown (CVE-2017-5753 and CVE-2017-5715).

Update to version 2.18.4:

 + Make WebDriver implementation more spec compliant.
 + Fix a bug when trying to remove cookies before a web process is
   spawned.
 + WebKitWebDriver process no longer links to libjavascriptcoregtk.
 + Fix several memory leaks in GStreamer media backend.
 + bsc#1073654 - Security fixes: CVE-2017-13866, CVE-2017-13870,
   CVE-2017-7156, CVE-2017-13856.

Update to version 2.18.3:

 + Improve calculation of font metrics to prevent scrollbars from being
   shown unnecessarily in some cases.
 + Fix handling of null capabilities in WebDriver implementation.
 + Security fixes: CVE-2017-13798, CVE-2017-13788, CVE-2017-13803.

Update to version 2.18.2:

 + Fix rendering of arabic text.
 + Fix a crash in the web process when decoding GIF images.
 + Fix rendering of wind in Windy.com.
 + Fix several crashes and rendering issues.

Update to version 2.18.1:

 + Improve performance of GIF animations.
 + Fix garbled display in GMail.
 + Fix rendering of several material design icons when using the web font.
 + Fix flickering when resizing the window in Wayland.
 + Prevent default kerberos authentication credentials from being used in
   ephemeral sessions.
 + Fix a crash when webkit_web_resource_get_data() is cancelled.
 + Correctly handle touchmove and touchend events in WebKitWebView.
 + Fix the build with enchant 2.1.1.
 + Fix the build in HPPA and Alpha.
 + Fix several crashes and rendering issues.
 + Security fixes: CVE-2017-7081, CVE-2017-7087, CVE-2017-7089,
   CVE-2017-7090, CVE-2017-7091, CVE-2017-7092, CVE-2017-7093,
   CVE-2017-7094, CVE-2017-7095, CVE-2017-7096, CVE-2017-7098,
   CVE-2017-7099, CVE-2017-7100, CVE-2017-7102, CVE-2017-7104,
   CVE-2017-7107, CVE-2017-7109, CVE-2017-7111, CVE-2017-7117,
   CVE-2017-7120, CVE-2017-7142.

• Enable gold linker on s390/s390x on SLE15/Tumbleweed.

This update was imported from the SUSE:SLE-12-SP2:Update update project.