Timeout with local html file
I was just testing something out simple with this and plugged in a basic html file

```html
<!DOCTYPE html>
<html lang="en">
  <title> </title>
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <link rel="stylesheet" href="https://unpkg.com/tachyons/css/tachyons.min.css">
  <body>
    <button data-sketch-symbol="Button/Primary" class="bw1-l br2 bg-dwyl-teal pa2 white fw1 tc ttu tracked">do what you love</button>
    <div data-sketch-text="Heading" class="f1 fw7 sans-serif lh-title">Headline 1</div>
    <div data-sketch-text="Body" class="sans-serif lh-copy">Body</div>
    <div data-sketch-color="#A463F2" class="pa4 bg-light-purple">&nbsp;</div>
  </body>
</html>
```

I followed the readme, but I'm getting a timeout error. Am I missing something?

```zsh
$ npm install --global html-sketchapp-cli
$ html-sketchapp --file index.html --out-dir .
Error: Timeout
    at Timeout._onTimeout (/usr/local/lib/node_modules/html-sketchapp-cli/node_modules/wait-on/lib/wait-on.js:92:10)
    at ontimeout (timers.js:458:11)
    at tryOnTimeout (timers.js:296:5)
    at Timer.listOnTimeout (timers.js:259:5)
```


