Bug fixes:

• Improve error message if a header contains an invalid character -- https://github.com/github/fetch/pull/880 Thank you for the contribution @CarmeloPatti

• Make Response.statusText be an empty string if set to undefined and be 'null' if set to null -- https://github.com/github/fetch/pull/897 Thank you for the contribution @tkrotoff

• Represent non-stringified JSON request body as an [object Object] string -- https://github.com/github/fetch/pull/881 Thank you for the contribution @kettanaito