* Change var to const in an example of server creation.
* Add missing semicolons.
* Use `console` syntax highlighting in `telnet` and `nc` invocation
  examples and add shell prompt symbols to be consistent with the rest
  of the documentation.

PR-URL: nodejs#11786
Reviewed-By: Luigi Pinca <[email protected]>
Reviewed-By: Joyee Cheung <[email protected]>
Reviewed-By: Colin Ihrig <[email protected]>
Reviewed-By: Anna Henningsen <[email protected]>
Reviewed-By: James M Snell <[email protected]>