WebCore fails to link in Chromium official build
https://bugs.webkit.org/show_bug.cgi?id=110701

Reviewed by Abhishek Arya.

This is a follow-up fix for r143853. In WebCore.gyp, we need to
increase the shard of 'webcore_rendering' as well.

No tests. No change in behavior.

* WebCore.gyp/WebCore.gyp:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@143855 268f45cc-cd09-0410-ab3c-d52691b4dbfc