Updates (#57)

* Travis CI: add Node.js 10.x.

* Move eslint mocha where it's needed.

* Update devDependencies.

Notes:

* package-lock.json is saved with npm 6.3.1, the one that ships with node.js 10.x
* eslint 5.x doesn't support node.js 4.x, so don't update it

test/index.js

@@ -1,3 +1,5 @@
+/* eslint-env mocha */
+
 const assert = require('assert');
 const binCheck = require('bin-check');
 const hugoBin = require('../');