Remove cp->set_variable for EE 2.8 compatibility

cp->set_variable was deprecated in 2.6 and removed in 2.8.x.

http://ellislab.com/expressionengine/user-guide/development/usage/cp.html#set-variables

When attempting to use cp->set_variable the module is unusable
Merge pull request #6 from zuDevonRW/patch-1

Remove cp->set_variable for EE 2.8 compatibility