Axios doesn't work in certain environments, consider using node fetch

[karthikb351]

Axios doesn't work in certain enviroments (like Cloudflare Workers). It would be good to use a more modern HTTP client like fetch or isomorphic-fetch instead.

I'm currently trying to use js-orbit-activities in a cloudflare workers environment, but axios doesn't work there. (but fetch does)

Ref:

• DefaultAdapter returns unknown/undefined by default axios/axios#2507
• https://community.cloudflare.com/t/can-i-use-axios-in-a-worker/168139