Update tutorial to use new HTTP API

[diggy (Dgraph Bot)]

Moved from GitHub tutorial/66

Posted by mangalaman93:

More details here Remove custom HTTP Headers, cleanup API by mangalaman93 · Pull Request #3365 · dgraph-io/dgraph · GitHub

[diggy (Dgraph Bot)]

paulftw commented :

Duplicate and fixes are already in the dgraph-1.1 branch.