Rename api.HTMLMarqueeElement.scrollamount -> scrollAmount (#7474)
Rename api.HTMLMarqueeElement.scrollamount -> scrollAmount (#7474)

This corrects capitalization for the HTMLMarqueeElement API's `scrollAmount` feature.
chrisdavidmills/browser-compat-data,mdn/browser-compat-data,chrisdavidmills/browser-compat-data,mdn/browser-compat-data