Just saw this after modifying ESLint config and running `yarn linc`:

```
/Users/gaearon/p/react/.eslintrc.js
  0:0  warning  File ignored by default.  Use a negated ignore pattern (like "--ignore-pattern '!<relative/path/to/filename>'") to override

✖ 1 problem (0 errors, 1 warning)

Lint failed for changed files.
error Command failed with exit code 1.
info Visit https://yarnpkg.com/en/docs/cli/run for documentation about this command.
react)            
```

We should not treat this particular warning as an error.
/**
 * Copyright (c) 2013-present, Facebook, Inc.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 */
'use strict';
const lintOnFiles = require('../eslint');
const listChangedFiles = require('../shared/listChangedFiles');
const changedFiles = [...listChangedFiles()];
const jsFiles = changedFiles.filter(file => file.match(/.js$/g));
const report = lintOnFiles(jsFiles);
if (report.errorCount > 0 || report.warningCount > 0) {
  console.log('Lint failed for changed files.');
  process.exit(1);
} else {
  console.log('Lint passed for changed files.');
}