docs: fix table-of-contents generation (#3840)

Author: aslushnikov

docs/api.md

@@ -690,7 +690,7 @@ page.removeListener('request', logRequest);
 ```
 
 <!-- GEN:toc -->
-- [event: '_videostarted'](#event-videostarted)
+- [event: '_videostarted'](#event-_videostarted)
 - [event: 'close'](#event-close-1)
 - [event: 'console'](#event-console)
 - [event: 'crash'](#event-crash)

docs/ci.md

@@ -15,7 +15,7 @@ configurations for common CI providers.
   * [Bitbucket Pipelines](#bitbucket-pipelines)
   * [GitLab CI](#gitlab-ci)
 - [Caching browsers](#caching-browsers)
-    - [Exception: `node_modules` are cached](#exception-nodemodules-are-cached)
+    - [Exception: `node_modules` are cached](#exception-node_modules-are-cached)
     - [Directories to cache](#directories-to-cache)
 - [Debugging browser launches](#debugging-browser-launches)
 - [Running headful](#running-headful)
@@ -102,7 +102,7 @@ Suggested configuration
    Chromium in non-headless mode (e.g. to test Chrome Extensions)
 1. If your project does not have `package-lock.json`, Travis would be auto-caching
    `node_modules` directory. If you run `npm install` (instead of `npm ci`), it is
-   possible that the browser binaries are not downloaded. Fix this with [these steps](#exception-nodemodules-are-cached) outlined below.
+   possible that the browser binaries are not downloaded. Fix this with [these steps](#exception-node_modules-are-cached) outlined below.
 
 To sum up, your `.travis.yml` might look like this:
 

utils/doclint/preprocessor/index.js

@@ -90,7 +90,7 @@ function getTOCEntriesForText(text) {
   for (const {line, offset} of titles) {
     const [, nesting, name] = line.match(titleRegex);
     const delinkifiedName = name.replace(/\[([^\]]+)\]\([^)]+\)/g, '$1');
-    const id = delinkifiedName.trim().toLowerCase().replace(/\s/g, '-').replace(/[^-0-9a-zа-яё]/ig, '');
+    const id = delinkifiedName.trim().toLowerCase().replace(/\s/g, '-').replace(/[^-_0-9a-zа-яё]/ig, '');
     let dedupId = id;
     let counter = 0;
     while (ids.has(dedupId))