pa11y-ci should use the puppeteer of pa11y

[masi]

Both packages have their own dependency on puppeteer. This causes npm to download puppeeteer once for pa11y and once for pa11y-cli.

At least that what happens to me when I have BackstopJS installed as well, which depends on a newer version of puppeteer (10.0.0 at the time of writing).

Sidenote: why does both packages do not depend on puppeteer-core? Then I could use any Chromium I want to.

[josebolos]

Pa11y-ci v3 now uses the same version of puppeteer than pa11y, so puppeteer will only be installed once.

Regarding the use of puppeteer-core, most of pa11y's usage happens in CI systems and we want to provide a tool that will work out of the box as much as possible. This also help us test pa11y releases and ensure that nothing will break if people choose to use a different Chromium version.