@function
@private

Validate the plugin's options

@param {string} host The host to filter by virtual host
@throws The options are invalid
function validate (host) {
  const hostScheme = joi.array()
    .items(joi.string().min(1))
    .min(1).single()

  joi.assert(host, hostScheme, 'The parameter `host` is invalid. Its')
}