Update rustls-pemfile requirement from 1.0 to 2.1 (#643)

* Update rustls-pemfile requirement from 1.0 to 2.1

Updates the requirements on [rustls-pemfile](https://github.com/rustls/pemfile) to permit the latest version.
- [Release notes](https://github.com/rustls/pemfile/releases)
- [Commits](rustls/pemfile@v/1.0.0...v/2.1.0)

---
updated-dependencies:
- dependency-name: rustls-pemfile
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

* update code

---------

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Dominic <[email protected]>

examples/hello_world_tls/Cargo.toml

@@ -7,4 +7,4 @@ edition = "2018"
 
 [dependencies]
 gotham = { path = "../../gotham", features = ["rustls"] }
-rustls-pemfile = "1.0"
+rustls-pemfile = "2.1"

examples/hello_world_tls/src/main.rs

@@ -1,6 +1,6 @@
 //! A Hello World example application for working with Gotham.
 use gotham::anyhow;
-use gotham::rustls::{self, Certificate, PrivateKey, ServerConfig};
+use gotham::rustls::{Certificate, PrivateKey, ServerConfig};
 use gotham::state::State;
 use rustls_pemfile::{certs, pkcs8_private_keys};
 use std::io::BufReader;
@@ -24,19 +24,19 @@ pub fn main() -> anyhow::Result<()> {
     Ok(())
 }
 
-fn build_config() -> Result<ServerConfig, rustls::Error> {
+fn build_config() -> anyhow::Result<ServerConfig> {
     let mut cert_file = BufReader::new(&include_bytes!("cert.pem")[..]);
     let mut key_file = BufReader::new(&include_bytes!("key.pem")[..]);
     let certs = certs(&mut cert_file)
-        .unwrap()
-        .into_iter()
-        .map(Certificate)
-        .collect();
-    let mut keys = pkcs8_private_keys(&mut key_file).unwrap();
+        .map(|result| result.map(|der| Certificate(der.to_vec())))
+        .collect::<Result<_, _>>()?;
+    let mut keys = pkcs8_private_keys(&mut key_file);
+    let key = PrivateKey(keys.next().unwrap()?.secret_pkcs8_der().to_vec());
     ServerConfig::builder()
         .with_safe_defaults()
         .with_no_client_auth()
-        .with_single_cert(certs, PrivateKey(keys.remove(0)))
+        .with_single_cert(certs, key)
+        .map_err(Into::into)
 }
 
 #[cfg(test)]