Support EXPOSE with SCTP protocol

[jameswmcnab]

Docker 18.03 added support for exposing SCTP ports for a container

This PR updates the validator to recognise EXPOSE 8080/sctp as valid.

Please let me know if I've missed anything.

[coveralls]

Coverage increased (+0.001%) to 98.446% when pulling 120ff0b on jameswmcnab:sctp-protocol into e10197f on rcjsuen:master.

[rcjsuen]

Hi, @jameswmcnab. Thank you very much for your pull request.

The code itself looks good and sound! For stylistic reasons, please do the following (by amending your commit and then force pushing up to your branch):

1. Add a note to the CHANGELOG.md under the "Added" section of the currently "Unreleased" bit at the top mentioning that this fixes Add support for SCTP in EXPOSE instruction #52. You can look at the many other entries in the changelog to get a feel of how I write these one-liners and the rough format it's in.
2. Amend your commit message to include Fix #52 in the beginning of the commit message.
3. In addition to 2, when amending your commit please also use -s so that we can get a Signed-off-by footer.

Thank you for your time and understanding!

[rcjsuen]

@jameswmcnab And, and I also forgot to mention to please update the bin/dockerfile-utils file.

dockerfile-utils/bin/dockerfile-utils

Lines 42 to 45 in e10197f

	function printVersion() {
	const package = require("../package.json");
	console.log("dockerfile-utils version " + package.version + " (supports Docker CE 17.09)");
	}

Please change the above function to print out Docker CE 18.03 instead of Docker CE 17.09. Thanks!

[jameswmcnab]

@rcjsuen Thanks! I've made the requested changes.

[rcjsuen]

@jameswmcnab Thank you for the quick turnaround and your wonderful contribution!