docs(CONTRIBUTING.md): fix some typos (#4917)
docs(CONTRIBUTING.md): fix some typos (#4917)

As someone who's new to the project, I read the contributing guide and spotted some things that confused me. Hopefully this patch helps to reduces the confusion for others!
GoogleChrome/puppeteer,puppeteer/puppeteer,GoogleChrome/puppeteer,puppeteer/puppeteer,puppeteer/puppeteer,puppeteer/puppeteer,GoogleChrome/puppeteer