Make ninja the default w/ build-webkit --chromium on windows.
https://bugs.webkit.org/show_bug.cgi?id=110731

Unreviewed - TBR'ing thakis :).

* Scripts/update-webkit-chromium:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@143978 268f45cc-cd09-0410-ab3c-d52691b4dbfc