fix #620 remove @-ms-keyframes

`@-ms-keyframes` doesn't make sense. It's not supported by any IE version. 

It just generates a lot of unnecessary CSS (for all browsers) which is then discarded.
IE10 supports unprefixed `@keyframes` and IE9 doesn't support it at all.

According to
https://developer.mozilla.org/en-US/docs/Web/CSS/@keyframes
Firefox supports unprefixed keyframes since 16.0. Opera 15 uses `-webkit` instead of `-o`. We could remove those (`-moz` and `-o`) also later on.