feat: TS v4, tslint -> eslint, add cspell support (#240)

Update all dependencies, migrate from tslint (deprecated) to typescript-eslint, and add support for
cspell.

BREAKING CHANGE: migrated from tslint (deprecated) to eslint.

src/lib/async.spec.ts

@@ -1,7 +1,7 @@
-// tslint:disable:no-expression-statement
 import test from 'ava';
+
 import { asyncABC } from './async';
 
-test('getABC', async t => {
+test('getABC', async (t) => {
   t.deepEqual(await asyncABC(), ['a', 'b', 'c']);
 });