update javascript fetch request to match node-fetch

[jonasholbech]

Vanilla JS did not return the json from the request, the node.js version does, now they should behave the same

[CLAassistant]

All committers have signed the CLA.

[erunion]

Can you update the tests for the JS target? They need this line added to them.

[jonasholbech]

Let me see if I can find those :-)

[erunion]

Here you go: https://github.com/Kong/httpsnippet/tree/master/test/fixtures/output/javascript/fetch

[jonasholbech]

thanks @erunion

[reynolek]

Thanks for the contribution @jonasholbech!