Fix srandmember spec on redis-rb >= 3.0.3

In 3.0.3, srandmember introduced an option[0] 'count' argument which causes
our `args_for_method` to generate invalid arguments.

I spent a while poking around, and there are enough assumptions about
the arity of different methods that there was no clean solution. Even
introducing the optional argument to `srandmember` doesn't fix the
issue: because the arity is now -2 (1 required argument), it gets an
invalid parameter list.

Longer term we should refactor how we determine method arguments.
Shorter term, the specs now pass on the most recent release of the
redis-rb gem.

[0] https://github.com/redis/redis-rb/commit/074f45edff63b3d80ed51dbff29276a4bd84a4da

Change-Id: I46296f6c1ed3c9f711244231dba77f1cec46e68f
Reviewed-on: https://gerrit.causes.com/19594
Reviewed-by: Aiden Scandella <aiden@causes.com>
Tested-by: jenkins <jenkins@causes.com>
Fix zrevrange to return empty array on invalid range

Change-Id: I023cfe1787aec4eecde21c47798da0d48c52ce59
Reviewed-on: https://gerrit.causes.com/19586
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Aiden Scandella <aiden@causes.com>