Deprecation warning with Rails 6

[packerbacker89]

Using caracal-rails with Rails 6 leads to the following deprecation warning:

DEPRECATION WARNING: Single arity template handlers are deprecated. Template handlers must
now accept two parameters, the view object and the source for the view object.
Change:
  >> Caracal::Rails::TemplateHandler.call(template)
To:
  >> Caracal::Rails::TemplateHandler.call(template, source)

[dwood-somniainc]

Yup. I get this error in my testing suite all of the time. Hopefully, he'll be able to update it soon.

[spovich]

This is a one-liner fix in this PR: #12

Verified this fixes the issue. Any chance of a new release?