Use `@libsql/isomorphic-fetch` for Deno and Workers compatibility

[honzasp]

Use our own @libsql/isomorphic-fetch package that is compatible with Node, Deno and Cloudflare Workers.

Fixes #16

[honzasp]

bors merge

[bors[bot]]

Build failed:

• Build and test on Node.js

[honzasp]

bors retry

[bors[bot]]

Build succeeded:

• Build and test on Node.js