Fix new clippy lints (#561)

src/unit.rs

@@ -87,7 +87,7 @@ impl Unit {
             if (!username.is_empty() || !password.is_empty())
                 && get_header(&headers, "authorization").is_none()
             {
-                let encoded = base64::encode(&format!("{}:{}", username, password));
+                let encoded = base64::encode(format!("{}:{}", username, password));
                 extra.push(Header::new("Authorization", &format!("Basic {}", encoded)));
             }