title: istambul nyc fails to detect any files when running ava test suite
body: <p>Started trying to integrate nyc/istambul into my ava test suites:</p>
  <pre class="lang-sh prettyprint-override"><code>./node_modules/.bin/nyc --include modules/todo.js --es-modules ./node_modules/.bin/ava
    1 tests passed
    ----------|---------|----------|---------|---------|-------------------
    File      | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s 
    ----------|---------|----------|---------|---------|-------------------
    All files |       0 |        0 |       0 |       0 |                   
    ----------|---------|----------|---------|---------|-------------------
  </code></pre>
  <p>The output fails to list any of the files!</p>
  <p>If I add the <code>--all</code> flag I get the following even though the tests cover both functions:</p>
  <pre><code>ERROR: Coverage for lines (0%) does not meet global threshold (90%)
  ----------|---------|----------|---------|---------|-------------------
  File      | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s 
  ----------|---------|----------|---------|---------|-------------------
  All files |       0 |        0 |       0 |       0 |                   
   todo.js  |       0 |        0 |       0 |       0 | 6-30              
  ----------|---------|----------|---------|---------|-------------------
  </code></pre>
  <p>So it looks as if the output from the <code>ava</code> testing tool is not being picked up by the <code>nyc</code> coverage tool.</p>
  <p>The simple setup is as follows:</p>
  <pre class="lang-js prettyprint-override"><code>/* todo.js (uses ES6 modules) */
  
  'use strict'
  
  let data = []
  
  function clear() {
      data = []
  }
  
  function add(item, qty = 1) {
      qty = Number(qty)
      if(isNaN(qty)) throw new Error('qty must be a number')
      data.push({item: item, qty: qty})
    return true
  }
  
  export { add, clear }
  </code></pre>
  <pre class="lang-js prettyprint-override"><code>/* todo.spec.js */
  import { add, clear } from './modules/todo.js'
  import test from 'ava'
  
  test('add a single item', test =&gt; {
    clear()
    const ok = add('bread')
    test.truthy(ok)
  })
  </code></pre>
  <p>I tried creating a <code>.nycrc.json</code> file but this didn't help:</p>
  <pre class="lang-json prettyprint-override"><code>{
    &quot;check-coverage&quot;: true,
    &quot;include&quot;: [
      &quot;modules/todo.js&quot;
    ],
    &quot;reporter&quot;: [&quot;text&quot;, &quot;html&quot;]
  }
  </code></pre>