chore: clean up remaining Travis references (#6826)

Issue: #6726

docs/troubleshooting.md

@@ -194,7 +194,7 @@ export CHROME_DEVEL_SANDBOX=/usr/local/sbin/chrome-devel-sandbox
 
 ## Running Puppeteer on Travis CI
 
-> 👋 We run our tests for Puppeteer on Travis CI - see our [`.travis.yml`](https://github.com/puppeteer/puppeteer/blob/main/.travis.yml) for reference.
+> 👋 We ran our tests for Puppeteer on Travis CI until v6.0.0 (when we've migrated to GitHub Actions) - see our historical [`.travis.yml` (v5.5.0)](https://github.com/puppeteer/puppeteer/blob/v5.5.0/.travis.yml) for reference.
 
 Tips-n-tricks:
 - [xvfb](https://en.wikipedia.org/wiki/Xvfb) service should be launched in order to run Chromium in non-headless mode

experimental/puppeteer-firefox/.npmignore

@@ -31,7 +31,6 @@ yarn.lock
 .editorconfig
 .eslintignore
 .eslintrc.js
-.travis.yml
 README.md
 tsconfig.json
 

utils/doclint/cli.js

@@ -129,7 +129,7 @@ async function run() {
   }
   console.log(`${errors.length} failures, ${warnings.length} warnings.`);
 
-  if (!clearExit && !process.env.TRAVIS)
+  if (!clearExit && !process.env.GITHUB_ACTIONS)
     console.log(
       '\nIs your lib/ directory up to date? You might need to `npm run tsc`.\n'
     );