Fix Dir.entries on ruby-2.1.0-preview2

Ruby 2.1's Dir.entries method now allows an "encoding" option.  Without this change, an ArgumentError is raised.

See also http://ruby-doc.org/core-2.1.0/Dir.html
Ensure rspec picks up the added spec.
Merge branch 'benjaminoakes/master'

* benjaminoakes/master:
  Ensure rspec picks up the added spec.
  Fix Dir.entries on ruby-2.1.0-preview2