Update to get wolverine working with the redis gem (redis-rb)

Hi,

I had some issues trying to get wolverine up and running so I dug deeper and found that the redis-rb implementation of eval and evalsha (actually _eval) only expect 2 arguments instead of the 3 that wolverine was passing through.

The number of keys don't need to be passed through since redis-rb simply gets it from the size of the keys array.

I looked through the redis-rb (master) history and it looks like eval and evalsha always expected 2 arguments, I assume that you built wolverine on a fork off master before they settled on the final implementation...

Anyway, I'd appreciate it if you could review/merge my pull request which updates wolverine to work with redis-rb.

Thanks,

Leo Venegas