Typo.

src/completer/widget.ts

@@ -195,7 +195,7 @@ class CompleterWidget extends Widget {
   }
 
   /**
-   * Handle `after_attach` messages for the widget.
+   * Handle `after-attach` messages for the widget.
    */
   protected onAfterAttach(msg: Message): void {
     document.addEventListener('keydown', this, USE_CAPTURE);

src/notebook/notebook/widget.ts

@@ -821,7 +821,7 @@ class Notebook extends StaticNotebook {
   }
 
   /**
-   * Handle `after_attach` messages for the widget.
+   * Handle `after-attach` messages for the widget.
    */
   protected onAfterAttach(msg: Message): void {
     super.onAfterAttach(msg);

src/toolbar/index.ts

@@ -189,7 +189,7 @@ class ToolbarButton extends Widget {
   }
 
   /**
-   * Handle `after_attach` messages for the widget.
+   * Handle `after-attach` messages for the widget.
    */
   protected onAfterAttach(msg: Message): void {
     this.node.addEventListener('click', this);