* array.c (rb_ary_uniq_bang): use rb_ary_modify_check() instead of
  rb_ary_modify() because the array will be unshared soon.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43472 b2dd03c8-39d4-4d8f-98ff-823fe69b080e