in src/main/scala/com/gu/fastly/api/FastlyApiClient.scala [86:90]
def purge(url: String, extraHeaders: Map[String, String] = Map.empty): Future[Response] = {
val urlWithoutPrefix = url.stripPrefix("http://").stripPrefix("https://")
val apiUrl = s"$fastlyApiUrl/purge/$urlWithoutPrefix"
AsyncHttpExecutor.execute(apiUrl, POST, headers = Map("Fastly-Key" -> apiKey) ++ extraHeaders)
}