prepare-ChangeLog reports as deleted methods that has not been removed.
https://bugs.webkit.org/show_bug.cgi?id=131733

Reviewed by Ryosuke Niwa.

* Scripts/prepare-ChangeLog:
(originalFile): Set merge base to origin/master by default.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@167753 268f45cc-cd09-0410-ab3c-d52691b4dbfc