ANSI colors not supported in the format

[Skywalker13]

Hello, the width is not computed correctly when ansi colors are used

https://github.com/tj/node-progress/blob/master/lib/node-progress.js#L139

ansi-regex should be considered, something like that

var ansiRegex = require('ansi-regex');

var availableSpace = Math.max(0, this.stream.columns - str.replace(ansiRegex(), '').replace(':bar', '').length);

[thebigredgeek]

Happy to review a PR!