Update openssl command to list digest algos in docs

Documentation update in https://nodejs.org/api/crypto.html#crypto_crypto_createhash_algorithm_options

The algorithm is dependent on the available algorithms supported by the version of OpenSSL on the platform. Examples are 'sha256', 'sha512', etc. On recent releases of OpenSSL, openssl list-message-digest-algorithms will display the available digest algorithms.

Replace the openssl command

openssl list-message-digest-algorithms

with

openssl list -digest-algorithms

Tested with:

$ openssl version
OpenSSL 1.1.0h  27 Mar 2018