Default port with configuration file

[ColinSullivan1]

If you use a configuration file, the default port of 9090 is not used.

To reproduce, just run with an empty config file.

$ touch oo.conf
$ nats-account-server -c oo.conf
2019/05/13 14:18:42.583273 [INF] loading configuration from "/Users/colinsullivan/go/src/github.com/nats-io/nats-account-server/oo.conf"
2019/05/13 14:18:42.583546 [INF] starting NATS Account server, version 0.0-dev
2019/05/13 14:18:42.583572 [INF] server time is Mon May 13 14:18:42 MDT 2019
2019/05/13 14:18:42.583583 [INF] creating an in-memory store
2019/05/13 14:18:42.583612 [INF] NATS is not configured, server will not fire notifications on update
2019/05/13 14:18:42.583961 [INF] http listening on port 61787
2019/05/13 14:18:42.583975 [INF] nats-account-server is running
2019/05/13 14:18:42.583980 [INF] configure the nats-server with:
2019/05/13 14:18:42.583992 [INF]   resolver: URL(http://127.0.0.1:61787/jwt/v1/accounts/)