Fix some typos. (#620)

src/data/graph.rs

@@ -370,7 +370,7 @@ impl<N, E> Graph<N, E> {
         // indices.
         let edge = self.edges.swap_remove(e.index());
         let swap = match self.edges.get(e.index()) {
-            // no elment needed to be swapped.
+            // no element needed to be swapped.
             None => return Some(edge.weight),
             Some(ed) => ed.node,
         };

src/data/pubsub.rs

@@ -103,7 +103,7 @@ impl<T> PubSub<T> {
         subscription
     }
 
-    /// Read the i-th message not yet read by the given subsciber.
+    /// Read the i-th message not yet read by the given subscriber.
     pub fn read_ith(&self, sub: &Subscription<T>, i: usize) -> Option<&T> {
         let cursor = &self.cursors[sub.id as usize];
         self.messages.get(cursor.next(self.deleted_messages) + i)