Dgraph-js-http setSlashApiKey breaks

Hi Team,

The client dgraph-js-http breaks when setting the Slash API key.

See dgraph-js-http/clientStub.js at master · dgraph-io/dgraph-js-http · GitHub

setSlashApiKey(apiKey) is missing the following to create headers if undefined.

this.options.headers === undefined && (this.options.headers = {});

Hence, one would get a TypeError: this.options.headers is undefined

I have submitted a PR Fix issue where setSlashApiKey would break if no headers was set. by Sydney-o9 · Pull Request #34 · dgraph-io/dgraph-js-http · GitHub

Thanks for the PR. I’ll get this merged and released shortly.