fix(deps): `tocbot` has no initialization detection (#957)

Resolves #957

_javascript/modules/components/toc.js

@@ -1,4 +1,5 @@
 export function toc() {
+  if (document.querySelector('#core-wrapper h2,#core-wrapper h3')) {
     // see: https://github.com/tscanlin/tocbot#usage
     tocbot.init({
       tocSelector: '#toc',
@@ -8,4 +9,5 @@ export function toc() {
       orderedList: false,
       scrollSmooth: false
     });
+  }
 }