common.mk: use BASERUBY

* common.mk (Doxyfile): tool/file2lastrev.rb needs running with
  BASERUBY since r43617.  [ruby-dev:47823] [Bug #9169]


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43888 b2dd03c8-39d4-4d8f-98ff-823fe69b080e