Updated dot example

Author: octavonce

examples/dot.rs

@@ -11,15 +11,24 @@ pub fn main() {
     let v2 = graph.add_vertex("test2".to_string());
     let v3 = graph.add_vertex("test3".to_string());
     let v4 = graph.add_vertex("test4".to_string());
-
     let v5 = graph.add_vertex("test5".to_string());
     let v6 = graph.add_vertex("test6".to_string());
 
+    #[cfg(feature = "dot")] 
+    {
+        graph.label_vertex(&v1, "test1").unwrap();
+        graph.label_vertex(&v2, "test2").unwrap();
+        graph.label_vertex(&v3, "test3").unwrap();
+        graph.label_vertex(&v4, "test4").unwrap();
+        graph.label_vertex(&v5, "test5").unwrap();
+        graph.label_vertex(&v6, "test6").unwrap();
+    }
+
     graph.add_edge(&v1, &v2).unwrap();
     graph.add_edge(&v3, &v1).unwrap();
     graph.add_edge(&v1, &v4).unwrap();
     graph.add_edge(&v5, &v6).unwrap();
 
     #[cfg(feature = "dot")]
-    graph.to_dot("example1", &mut f);
+    graph.to_dot("example1", &mut f).unwrap();
 }