Auto-hide navigation on link click (#1238)

Hide navigation sidebar when clicking anchor links on mobile devices.
Previously, anchor links would change the page but the navigation
sidebar would block the view.

lib/rdoc/generator/template/darkfish/js/darkfish.js

@@ -103,6 +103,12 @@ function hookSidebar() {
   if (isSmallViewport) {
     navigation.hidden = true;
     navigationToggle.ariaExpanded = false;
+    document.addEventListener('click', (e) => {
+      if (e.target.closest('#navigation a')) {
+        navigation.hidden = true;
+        navigationToggle.ariaExpanded = false;
+      }
+    });
   }
 }