Update 'connection_pool' dependency to ~> 1.0.0

This lets the newest 'sidekiq' gem (and others) work with this.

Change-Id: I55f202b2c31e69cea100db1139f0968e6643d160
Reviewed-on: http://review.couchbase.org/26638
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Tested-by: Sergey Avseyev <sergey.avseyev@gmail.com>