Wrong value in the type of "score" in the "Understanding result" documentation

[khalyomede]

Explaination
I noticed your documentation is mentionning the score of one of the key report.lhr.categories.{}.score as String, but it appears in my console as Number.

Reproduce the issue

1. Go to the documentation : https://github.com/GoogleChrome/lighthouse/blob/master/docs/understanding-results.md#categoryentry-properties
2. See that the type of the score cell is String

Expected result
The documented type should be Number instead of String.

Note
I noticed it when I printed the score of the "performance" key for one of my lighthouse run for my website.

[patrickhulce]

Thanks @khalyomede! Interested in a PR? :)

[khalyomede]

Sure @patrickhulce! On my way. :)

[kaushikchaubal]

@khalyomede / @patrickhulce - i have created a PR for this. This is my first PR to this community so if anything looks wrong, please shout out.