Update dependency 'connection_pool' to '~> 1.0.0'

Change-Id: Ifaed7b28314dcaccd295dc5bd85a46113fe57af0
Reviewed-on: http://review.couchbase.org/26514
Tested-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Reviewed-by: Matt Ingenthron <matt@couchbase.com>