Don't work on server

[mcanobbio]

I tried use and when try to call function iapReceiptValidator get the error

fetch is not defined

I had to do a fork and add fetch-node npm and import on src/index.js and works perfect

idk how to detect if the environment is front or node-server to make a PR, if anyone helps me with that, i'll do a PR for add support to node-server

[akshetpandey]

You should be using this library instead for server stuff https://github.com/voltrue2/in-app-purchase

[sibelius]

U need to polyfill fetch to this package works well, we should add it to the README