mustache-express caches templates by default unless Express's `view
cache` option is explicitly set to `false`, as opposed to merely being
unset. This is not mentioned in the documentation :(

I debated whether to replace the mustache-express dependency with a
custom integration. mustache-express does provide support for partials
though which might be useful in future. For future reference, rendering
templates without this dependency would look like:

```js
app.engine('mustache', async (filePath, options, callback) => {
  try {
    const template = await fsPromises.readFile(filePath, {
      encoding: 'utf8',
    });
    const rendered = Mustache.render(template, options);
    callback(null, rendered);
  } catch (err) {
    callback(err);
  }
});
```