Be sure not to fill paths

src/lib.rs

@@ -165,7 +165,7 @@ impl AsSVG for Line {
 
             xml_tag(
                 buf, "path",
-                &[("d", &path), ("stroke", &"black")],
+                &[("d", &path), ("stroke", &"black"), ("fill", &"none")],
             );
         }
     }