add support for legacy-style timeouts on blocking list commands

The redis-rb gem 3.x still supports 2.x-style timeout arguments, so
we should too. This ensures that if the timeout is specified as an integer,
instead of a {timeout: Integer} hash, it is still recognized as a timeout.

[Resque](https://github.com/resque/resque) still uses the legacy timeout method signature, and the 0.13.0 release broke our build; we have since pinned to 0.12.x, but this is an attempt to get us back onto the current release.