Fix typo in error string

lettre/src/smtp/mod.rs

@@ -112,7 +112,7 @@ impl SmtpTransportBuilder {
                        timeout: Some(Duration::new(60, 0)),
                    })
             }
-            None => Err(From::from("Could nor resolve hostname")),
+            None => Err(From::from("Could not resolve hostname")),
         }
     }