use node-redis with node 8 util.promisify

If you are using node v8 or higher, you can promisify node_redis with util.promisify as in:

const {promisify} = require('util');
const getAsync = promisify(client.get).bind(client); // now getAsync is a promisified version of client.get:

// We expect a value 'foo': 'bar' to be present
// So instead of writing client.get('foo', cb); you have to write:
return getAsync('foo').then(function(res) {
    console.log(res); // => 'bar'
});

or using async await:

async myFunc() {
    const res = await getAsync('foo');
    console.log(res);
}

culled shamelessly from redis official repo

changing let get = util.promisify(client.get);

to let get = util.promisify(client.get).bind(client);

solved it for me :)