#69 fix multiple extensions issue

[aboutlo]

@jmav reported an issue with multiple extends in the #69 PR
I added the fix and the tests to cover that

Checklist

• run npm run test and npm run benchmark
• tests and/or benchmarks are included
• commit message and code follows [Code of conduct

[aboutlo]

Hey @jmav and @kieranczer I released [email protected] as release candidate
npm install [email protected]
yarn add [email protected]

let me know :)

[kieranczer]

Hey @jmav and @kieranczer I released [email protected] as release candidate
npm install [email protected]
yarn add [email protected]

let me know :)

Works great for my use case, although I can't speak for others. Thanks for getting to this so quickly!