Update type variables in documentation
Update type variables in documentation

Looks like this commit changed a lot of the type variable names
https://github.com/gcanti/fp-ts/commit/7bda18e34eed996a08afdd6a0a61025087f99593#diff-dccd8b3f1d6a82046698bcefd53a06a7
There were a few that got overlooked
gcanti/fp-ts,gcanti/fp-ts