Update dependency isomorphic-unfetch to v4

[renovate]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
isomorphic-unfetch	^3.1.0 -> ^4.0.2

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Release Notes

developit/unfetch (isomorphic-unfetch)

v4.0.2

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v4.0.1

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Quick publishing fix.

v4.0.0

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🦄 Small breaking change for awesome ponyness:

• unfetch is now a pure ponyfill.
• unfetch/polyfill is now the polyfill version (even smaller than the ponyfill!)
• All modules are shipped in all formats, and the polyfill is now < 500b.
• Also a little bugfix for IE11 (#​85, thanks @​khusa)

TL;DR: require('unfetch') no longer returns window.fetch when it exists. For that, use unfetch/polyfill.

This change makes unfetch lovely to use as a polyfill from HTML:

<script src="https://unpkg.com/unfetch/polyfill"></script>
<!-- that's it! -->
<script>foo = await fetch('/foo.json')</script>

Otherwise, if you're using Unfetch and bundling your code, continue as you were before:

if (!self.fetch) self.fetch = require('unfetch');
// or simply:
import 'unfetch/polyfill';

Important - the one thing to avoid:

Since unfetch is a proper ponyfill, it will now overwrite fetch even in supported browsers if you do the following

// never do this!
window.fetch = require('unfetch');

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