Fix Cache-Control header

Author: jdno

src/caching.rs

@@ -15,7 +15,7 @@ impl CachedNamedFile {
             file,
             header: Header {
                 name: Uncased {
-                    string: "CacheControl".into(),
+                    string: "Cache-Control".into(),
                 },
                 value: format!("max-age={max_age}").into(),
             },