Updates for new versions of Ruby.

No functional changes, updating dependancies and language syntax for new ruby versions. Deprecating Ruby 1.9.3 support.

v0.2.1

• See #7 for details.
• See https://rubygems.org/gems/maxcdn/versions/0.2.1 for gem.

v0.1.5

• Issue #4: Fixing purge files by array to return a hash of status results.

v0.1.4

Fixing bug where file purges purge entire zone.