Set allow(dead_code) on get_attribute

Signed-off-by: Adam Cattermole <[email protected]>

src/attribute.rs

@@ -104,6 +104,7 @@ impl Attribute for DateTime<FixedOffset> {
     }
 }
 
+#[allow(dead_code)]
 pub fn get_attribute<T>(f: &Filter, attr: &str) -> Result<T, String>
 where
     T: Attribute,