Fix doc example for early doc release

src/traits.rs

@@ -222,6 +222,7 @@ pub trait IncidenceCursor<G: GraphTopology + ?Sized> {
     /// ```
     /// # use grapherity::prelude::*;
     /// # use grapherity::models::Graph;
+    /// # use grapherity::traits::IncidenceCursor;
     /// // Constructs a graph with two vertices connected to `v`.
     /// let mut graph = Graph::new();
     /// let v = graph.add_vertex();