Fix progress bar colors in IE

[rafeememon]

This is a bugfix for progress bar colors in IE.

Proposed solution

This PR adds the necessary ::-ms-fill declarations to style the progress bar in IE, as explained here: https://developer.mozilla.org/en-US/docs/Web/CSS/::-ms-fill

Fixes #1333.

Tradeoffs

This slightly increases the size of the build, but improves support for IE. There are other -ms-* declarations in the code base so I think it is reasonable to add this.

Testing Done

I built my branch of Bulma locally, added it to my project, removed my workaround, and confirmed that the progress bar color can be changed:

[rafeememon]

Thanks!