Add feature flag rustls-tls for custom ca feature

src/ctx.rs

@@ -28,7 +28,7 @@ impl Ctx {
  fn http_client(read_timeout: Option<Duration>) -> Result<ureq::Agent, Error> {
  let mut builder = ureq::builder();
 
- #[cfg(feature = "native-tls")]
+ #[cfg(any(feature = "native-tls", feature = "rustls-tls"))]
  'custom: {
  // "common"? env vars that people who use custom certs use? I guess
  // this is easy to expand if it's not the case. /shrug