fix: isSupported when feature name is not in db

[cloudfroster]

Bug

when use

isSupported('notTheCssName', 'chrome')

occur error : Cannot read property 'stats' of undefined

break change

no

[Nyalab]

if the feature name does not exist, we should throw a ReferenceError, not fail silently, could you revise the code so it does that please?

if you look at the isSupported tests, the third one should test that in theory, why does it not work?

(you need to rebase your work on master so it works with the current version of caniuse-lite)

[neenhouse]

This is implemented in a better version here: #90