allow different ruby versions and fix tests

for https://github.com/FinalCAD/finalcloud/issues/3146
Pathname doesn't work in ruby 2.0....

On Thursday, October 23, 2014, Joel AZEMAR <notifications@github.com> wrote:

> In lib/content_caching/adapters/fs.rb:
>
> > @@ -12,7 +12,7 @@ def url document_url
> >        end
> >
> >        def delete document_path
> > -        Pathname(url(document_path)).delete
> > +        File.delete url(document_path)
>
> @s12chung <https://github.com/s12chung> i really prefer Pathname, but
> anyway...
>
> —
> Reply to this email directly or view it on GitHub
> <https://github.com/FinalCAD/content_caching/pull/1/files#r19261622>.
>