Remove black line from progress bar in IE (#1342)

sass/elements/progress.sass

@@ -20,6 +20,7 @@ $progress-value-background-color: $text !default
     background-color: $progress-value-background-color
   &::-ms-fill
     background-color: $progress-value-background-color
+    border: none
   // Colors
   @each $name, $pair in $colors
     $color: nth($pair, 1)