chore: clippy fixes

Author: link2xt

src/authentication.rs

@@ -103,11 +103,11 @@ impl Mechanism {
                 let decoded_challenge =
                     challenge.ok_or(Error::Client("This mechanism does expect a challenge"))?;
 
-                if vec!["User Name", "Username:", "Username"].contains(&decoded_challenge) {
+                if ["User Name", "Username:", "Username"].contains(&decoded_challenge) {
                     return Ok(credentials.authentication_identity.to_string());
                 }
 
-                if vec!["Password", "Password:"].contains(&decoded_challenge) {
+                if ["Password", "Password:"].contains(&decoded_challenge) {
                     return Ok(credentials.secret.to_string());
                 }
 

src/smtp_client.rs

@@ -262,7 +262,7 @@ impl<S: BufRead + Write + Unpin> SmtpTransport<S> {
             // Log the message
             debug!(
                 "status=sent ({})",
-                result.message.get(0).unwrap_or(&"no response".to_string())
+                result.message.first().unwrap_or(&"no response".to_string())
             );
         }