Port number isnt passed through

Hi guys

Noticed that the port number isnt passed through to Knex in your connection.js

e.g. if I change code to add port I can now connect to my non-standard mysql (1441) otherwise I get ECONNREFUSED as it uses default port (3306)

      if (protocol === 'sqlite3') {
        connection_info = {
          filename: database_url.host || ':memory:'
        };
      } else {
        connection_info = _.extend({
          host: database_url.hostname,

This is the line I added

          port: database_url.port,

          database: database_url.database,
          charset: 'utf8'
        }, database_url.parseAuth() || {});
      }

Could be dangerous for those hoping to reach a dev DB with a dev connection string!

Let me know if you want a pull request as would be nice to contribute something small to this great project, but looks like something simple for you guys, and Im not sure how to test