security issue: use alternative to isomorphic-fetch dependency

[shazron]

The library does not seem maintained, especially since it depends on node-fetch which has a security issue that is still unpatched:
matthew-andrews/isomorphic-fetch#204

The last release for isomorphic-fetch is Sep 2020, about 16 months ago.

[shazron]

matthew-andrews/isomorphic-fetch#204 (comment) cross-fetch seems to be a drop-in alternative

[shazron]

closed via #96