Prefer Enumerable#grep to filter by type

[olleolleolle]

This reformulates a tiny part of the code to use an existing Ruby method.

[netlify]

✅ Deploy Preview for lookbook-docs canceled.

Name	Link
🔨 Latest commit	59788dc
🔍 Latest deploy log	https://app.netlify.com/sites/lookbook-docs/deploys/64870cd5efb798000812c413

[allmarkedup]

Hey @olleolleolle, really sorry it's taken me so long to take a look at this.

I did not know about Enumerable#grep but this is so much nicer, thank you! The only problem is now I want to go through all my Ruby code to see where I can use it to clean things up a bit... :)

Will merge now, much appreciated.