in src/main/scala/com/gu/fastly/api/FastlyApiClient.scala [136:141]
def versionComment(version: Int, comment: String): Future[Response] = {
val apiUrl = s"$fastlyApiUrl/service/$serviceId/version/$version"
val headers = Map("Content-Type" -> "application/x-www-form-urlencoded")
val params = Map("comment" -> comment)
AsyncHttpExecutor.execute(apiUrl, PUT, headers = commonHeaders ++ headers, parameters = params)
}