Upgrade gems to fix problem with broken content

The older versions of httparty and json made all downloaded files break
as the encoding was completely screwy when run on ruby 2.1.1 (and
possible others).

This patch also fixes #70 and #92.
Merge pull request #95 from peterhoeg/upgrade_httparty_and_json_to_fix_broken_content

Upgrade gems to fix problem with broken content