docker-container-id

This is a simple function to get the id of the docker container the
current process is running in. Not tested for Windows containers.

``
npm install --save docker-container-id
`

The function returns a promise for the conatiner id.

`js
const getId = require('docker-container-id');

async function() {
console.log("I'm in container:", await getId());
}
`

If you don't appear to be in a docker container, the promise resolves
with false:
`js
const getId = require('docker-container-id');

async function() {
let id = await getId();
if (!id) {
console.error("Woah, you need to containerize this thing!");
process.exit(1);
} else {
// ...
}
}
``