docs: add missing session cookie property to api.md (#1672)
docs: add missing session cookie property to api.md (#1672)

The session value is returned from the protocol, but not accepted as a cookie parameter.

Fixes #980.
GoogleChrome/puppeteer,GoogleChrome/puppeteer,puppeteer/puppeteer,puppeteer/puppeteer,GoogleChrome/puppeteer,puppeteer/puppeteer,puppeteer/puppeteer