Avoid using Binding#receiver

This feature is only available on Ruby 2.2+ and breaks older rubies.

See <https://docs.ruby-lang.org/en/2.2.0/NEWS.html> for more details.

Author: ivoanjo

lib/ruby2_keywords.rb

@@ -11,7 +11,7 @@ def ruby2_keywords(name, *)
   end
 end
 
-main = TOPLEVEL_BINDING.receiver
+main = TOPLEVEL_BINDING.eval('self')
 unless main.respond_to?(:ruby2_keywords, true)
   # call-seq:
   #    ruby2_keywords(method_name, ...)

test/test_keyword.rb

@@ -22,7 +22,7 @@ def test_module_ruby2_keywords
   end
 
   def test_toplevel_ruby2_keywords
-    main = TOPLEVEL_BINDING.receiver
+    main = TOPLEVEL_BINDING.eval('self')
     assert_send([main, :respond_to?, :ruby2_keywords, true])
     assert_operator(main.method(:ruby2_keywords).arity, :<, 0)
   end