groupings render fix

fixes: #3 cli version doesn't render signal groupings

Making it work

v0.3.0

0.3.0

Initial release of CLI tool using PhantomJS

1. Download and install phantomJS v2 or newer from here: http://phantomjs.org/download.html
2. Download wavedrom-cli.js file.
3. Run: phantomjs wavedrom-cli.js -i diagram.js -p diagram.png -s diagram.svg