docs(api.md): fix sample code in API doc, `request.url` -> `request.url()` (#1889)
docs(api.md): fix sample code in API doc, `request.url` -> `request.url()` (#1889)


puppeteer/puppeteer,puppeteer/puppeteer,puppeteer/puppeteer,GoogleChrome/puppeteer,GoogleChrome/puppeteer,puppeteer/puppeteer,GoogleChrome/puppeteer