Rename hash argument to keyword argument
Rename hash argument to keyword argument

I think, the term "keyword argument" is more common and well established, than the term "hash argument". Most of the articles, that describe the feature, introduced in Ruby 2.0 use the term "keyword argument":

* [Ruby 2 Keyword Arguments](https://robots.thoughtbot.com/ruby-2-keyword-arguments)
* [Fun With Keyword Arguments, Hashes, and Splats](https://www.justinweiss.com/articles/fun-with-keyword-arguments/)
barsoom/attr_extras