Fixed suggestion in documentation resulting in linting error 'variables should be a map of key-valued strings'

Documentation now suggests a valid option with the intended result.

See #3147 

`"yes"`, opposed to `yes` is not casted to a boolean. `variables` only accepts key-valued strings.

Better solution would be to change the parsing of `variables` (allow boolean or check the actual value of the string).



See merge request !1660