Don't shadow value variable

I was getting this warning:

    .../fakeredis-0.5.0/lib/redis/connection/memory.rb:407: warning: shadowing outer local variable - value

It's not really a problem because the `value` variable doesn't get used again in this function.
Use result variable

I was getting this warning:

    .../fakeredis-0.5.0/lib/fakeredis/sort_method.rb:22: warning: assigned but unused variable - result

There's no reason to do the work twice. Getting rid of `result` would've worked too.
Merge pull request #117 from tfausak/fix-warnings

Fix warnings