Release v1.2.2 - 2016-03-31

References: #18, #19

• Removed hard dependency on json >= 1.8.1. Replaced with json_pure >= 1.8.1.
  The runtime will still attempt to load the faster gem, if availble and will fall
  back on json_pure for compatability. Ruby 2.0+ ships with 1.8.1 by default,
  so only Ruby 1.9.3 will default to the slower version.

  See related GitHub issue #18.