Add support for Emacs 27

[nikty]

Hello! It is not possible to use this package on Debian 11 without modifications because it requires Emacs 28.1. Emacs 27.1 is still vastly used and not really ancient. Please consider requiring Emacs 27.1:

;;; Package-Requires: ((emacs "27.1"))

[redguardtoo]

looks only unit test code are using 28+ api. You can use js-comint.el directly in emacs 27.

[nikty]

Right, but I can't install it using standard method of package-install.

[redguardtoo]

M-x package-install-file, or set up load-path, see https://www.gnu.org/software/emacs/manual/html_node/eintr/Loading-Files.html