ext/depend: fix dependency

* ext/depend (ENCOBJS, TRANSOBJS): fix header dependency, VPATH has
  $(srcdir)/include/ruby but not $(srcdir)/include, so cannot find out
  ruby/ruby.h.  use ruby.h instead and ../ruby for include/ruby.h.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@40186 b2dd03c8-39d4-4d8f-98ff-823fe69b080e