Update dependency isomorphic-unfetch to v3.1.0

[renovate[bot]]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
isomorphic-unfetch	3.0.0 -> 3.1.0

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Release Notes

developit/unfetch

v3.1.0

Compare Source

Also released: [email protected] - now with node-fetch 2.x, TypeScript definitions and a readme.

• TypeScript definitions!
• Fixes a bug in response status code parsing
• Fixes XHR being potentially synchronous in really old browsers
• Fixes parsing of empty header values
• Serves up the umd bundle on unpkg.com

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