fix: rename then to andThen (ramda#2772)

BREAKING CHANGE

The addition of R.then in Ramda 0.26 made the R object
a Promise-like object, and meant that Promise.resolve() will attempt
to resolve it by calling the then() method. R is not a Promise, and
to reassure JavaScript of this fact, R.then is renamed to R.andThen.

Version 0.26.1

Version 0.26.0

Version 0.26.0

Version 0.25.0

Version 0.24.1

Version 0.24.0

Version 0.23.0

Version 0.22.1

Version 0.22.0