Disable mash warnings (review catch up)

[unasuke]

original pull request description ( by @hnmx4 )

for #243.
I use a Hashie developer’s solution that solves issue similar to issue#243 as reference.

hashie/hashie#394

I just released Hashie v3.5.2 which has the disable_warnings feature for the Mash logger and sets the Hashie logger to the Rails logger when we detect that we're running in Rails. Hopefully, this helps!

https://github.com/intridea/hashie

You can also disable the logging in subclasses of Mash:

class Response < Hashie::Mash
  disable_warnings
end

---

I added commits for @sue445 's comment

I prefer add require 'itamae/mash' to lib/itamae.rb than here.

#244 (comment)

[sue445]

LGTM!

[unasuke]

YAY!