Update MissingExportEquals.md for import default = fetch

[benasher44]

It seems that in the case where export default fetch and fetch refers to a namespace and something else being merged with that namespace, one has to add something like this to the namespace:

import _default = fetch;
export { _default as default };

whereas today, the recommendation is:

const _default = typeof fetch;
export { _default as default };

It would be great to update MissingExportEquals.md to cover this namespace edge case.

[andrewbranch]

Let’s see if anything blows up after the @types/node-fetch merge 😄 If nobody complains after a couple days, I agree.

[andrewbranch]

@benasher44 would you want to open a PR?

[benasher44]

I'm somewhat interested, but I won't have time for the next 4-6 weeks, most likely.