load.c: tweak the return value

* load.c (rb_require_internal): tweak the return value, 1 and 0
  correspond to true and false in Kernel#require, respectively.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@48697 b2dd03c8-39d4-4d8f-98ff-823fe69b080e