Apply suggestions from code review

Co-authored-by: Mathias Bynens <mathias@qiwi.be>

CONTRIBUTING.md

@@ -274,12 +274,12 @@ See [Debugging Tips](README.md#debugging-tips) in the readme.
 The following steps are needed to update the Chromium version.
 
 1. Find a suitable Chromium revision
-   Not all revisions has builds for all platforms, so we need to find one that does.
+   Not all revisions have builds for all platforms, so we need to find one that does.
    To do so, run `utils/check_availability.js -rb` to find the latest suitable beta Chromium revision (see `utils/check_availability.js -help` for more options).
-2. Update `src/revisions.ts` with the found revision number.
-3. Run `npm run ensure-correct-devtools-protocol-revision`.
-   If it fails, update `package.json` with the expected `devtools-protoocol` version.
-4. Run `npm run tsc` and `npm install` and ensure that all tests pass.
+1. Update `src/revisions.ts` with the found revision number.
+1. Run `npm run ensure-correct-devtools-protocol-revision`.
+   If it fails, update `package.json` with the expected `devtools-protocol` version.
+1. Run `npm run tsc` and `npm install` and ensure that all tests pass. If a test fails, bisect the upstream cause of the failure, and either update the test expectations accordingly (if it was an intended change) or work around the changes in Puppeteer (if it’s not desirable to change Puppeteer’s observable behavior).
 
 ## Releasing to npm