Flow ignores dotfiles

Running `flow` in a project that has `.eslintrc.js` or any other JS dotfile will silently skip these files, even if they have the `@flow` pragma.

Even `flow check .eslintrc.js` silently fails. As a test, run `flow check .test.js` with the following content:

```js
/* @flow */

const num: number = 'string'
```