Switch gem source to 'https://rubygems.org'.
Small README fix.
Update queue_classic to 2.2.0
Use built-in JSON, like queue_classic does.
Update test helper.
Link to queue_classic repo in README.
Convert args to text type for comparison.

This is necessary as PostgreSQL 9.2 can't perform comparisons on the
JSON data type, which queue_classic now uses as default for the args
column.
Add note about args comparison to README.
Version 0.1.0