Update doc/expressionLanguage.md
Update doc/expressionLanguage.md

Co-authored-by: Fermín Galán Márquez <a42853be7dd7164f3322943925c40e0cb15f30bb@users.noreply.github.com>
telefonicaid/iotagent-node-lib,telefonicaid/iotagent-node-lib,telefonicaid/iotagent-node-lib