doc: fix version history for Loaders API
FWIW https://github.com/nodejs/node/pull/15445 introduced a --loader
flag (which landed in 8.8.0), and https://github.com/nodejs/node/pull/29752 renamed it to --experimental-loader
(which landed in 12.11.1).
https://github.com/nodejs/node/pull/37468 changed greatly the API, and IMO it's useful to have it documented somewhere.
//cc @nodejs/loaders