Schema introspection with node-fetch breaking change in 2.23.1

[gaelollivier]

It seems that commit c91e577 introduces a breaking change in using introspectSchema with a custom fetcher, such as node-fetch.
The code in the documentation would break, since query is now a parsed AST instead of a string, resulting in an object being sent.

I'm not sure this commit should have been published as a patch since it introduces a breaking change.

Side note: This change actually broke a build on the project I'm working on and allowed me to find an issue with my Dockerfile which was not properly using yarn.lock ^^'

[purdrew]

Ran into the same issue on my project. Thankfully the fix on my end is minimal but definitely should not have been a patch release and the documentation should be updated.

[stubailo]

We should make sure the docs are correct.

[hwillson]

Fixed in #933 - thanks!