Omit port from SockJS URL if not available. GH-46.

The document.location.port may be the empty string on IE
when a default port is being used. In that case, avoid
putting a port, or colon, in the URL to prevent a SyntaxError
during WebSocket construction.
Fix newly-discovered lint error in jshint@2.1.2.
Merge pull request #47 from reid/fix-websocket-syntaxerror

Omit port from SockJS URL if not available. GH-46.