Update IE data for CSSKeyframesRule API (#6911)
Update IE data for CSSKeyframesRule API (#6911)

This commit updates the IE data for the CSSKeyframesRule API based
upon results from the collector.  Additionally (with manual testing),
I found that IE supported the `appendRule` feature with its normal
name, never under the `insertRule` alt. name.
mdn/browser-compat-data,chrisdavidmills/browser-compat-data,chrisdavidmills/browser-compat-data,mdn/browser-compat-data