devel/rubygem-sidekiq-limit_fetch: change RUN_DEPENDS

Switch RUN_DEPENDS from devel/rubygem-sidekiq4 to
devel/rubygem-sidekiq because it works just fine with the
actual version. Also this prevents some conflicting
scenarios between rubygem-sidekiq usage.

Submitted by: Matthias Fechner <idefix@fechner.net>