Fixed deprecated port problem.

A la this commit
https://github.com/conformal/btcwire/commit/c4135db7288579b2503007d1de88936e33d90033
to conformal/btcwire the MainPort was moved to conformal/btcnet. This
changed the API and cause btc-crawl not to be go-get-able.
Merge pull request #1 from dkua/fix-port

Fixed deprecated port problem.