updated has_remaining_performs_key to use set

has_remaining_performs_key was using two commands to try and establish a lock.  In production I found this to be error prone.  I changed the code to use the latest form set which will set an expiration and only set the key if it doesn't exist.  This is the preferred way to establish a lock using redis per the documentation. http://redis.io/commands/set
fixed specs, fix deprecated warnings for rspec
Merge pull request #6 from johnnyiller/master

updated has_remaining_performs_key to use set