Merge pull request #1360 from MITx/edz/feature/explicit-css-charset

adding explicit charset declaration to additional css

lms/static/sass/course.scss

+@charset "UTF-8";
 @import 'bourbon/bourbon';
 
 @import 'base/reset';

lms/static/sass/ie.scss

+@charset "UTF-8";
 @import "bourbon/bourbon";
 @import "base/variables";