Add support for using <lang> dict when <lang-COUNTRY> dict is missing

[serpro69]

This was removed in #129 ( 3a9dde0 ) due to changes in fr and ja dicts - they became directories rather than single files.
Therefore it got a bit complicated to handle cases like:

faker {
  fakerConfig {
    locale = "fr-FR"
  }
}

where fr-FR.yml does not exist and would default to using fr.yml