send private method instead of calling it and raising an error

fixes:

beezo:~ ej$ irb
2.0.0-p247 :001 > require 'to_wkt_'
NoMethodError: private method `include' called for Array:Class
	from /Users/ej/.rvm/gems/ruby-2.0.0-p247/gems/to_wkt_-0.1.2/lib/to_wkt_.rb:18:in `<top (required)>'