Webpack's `require.context` not being employed

Related/original report: https://github.com/pahen/madge/issues/117

It appears Precinct does not work with webpack's dynamic loading with [require.context](https://webpack.github.io/docs/context.html) (basically glob) so e.g.

```javascript
var context = require.context(".", true, /\.js$/)
context.keys().forEach(context)
```

This ought to load all the modules with /\.js$/ from the current directory (".") and subdirectories (that's what the `true` specifies).

It does not appear to do so, at least via Madge/node-dependency-tree, and I did not see any mention of it in the Precinct code.

Just a heads up.

🍻