fix url for asio submodule
fix url for asio submodule

Change-Id: If1f0a9ab8bd9ef470bf0041502f52f1a643243a0
Reviewed-on: http://review.couchbase.org/c/couchbase-ruby-client/+/128654
Tested-by: Sergey Avseyev <87f6d5e4fd3644c3c20800cde7fd3ad1569370b3@gmail.com>
Reviewed-by: Sergey Avseyev <87f6d5e4fd3644c3c20800cde7fd3ad1569370b3@gmail.com>

couchbase/couchbase-ruby-client,couchbase/couchbase-ruby-client,couchbase/couchbase-ruby-client