fix(clippy): Fix needless_return lint. (#405)

This happens when building with `--features fancy`.

src/highlighters/mod.rs

@@ -92,7 +92,7 @@ impl Default for MietteHighlighter {
     }
     #[cfg(not(feature = "syntect-highlighter"))]
     fn default() -> Self {
-        return MietteHighlighter::nocolor();
+        MietteHighlighter::nocolor()
     }
 }