message: fix(button): fix space between text and icon
  This change fix the space between text and icon in `<bx-btn>`. When a
  button has a text as well as an icon, the distance of the text and the
  right edge of the button should have been `60px`.
diff: @@ -25,7 +25,7 @@ $css--plex: true !default;
  ::slotted([slot='icon']) {
  fill: currentColor;
  - margin-left: $carbon--spacing-03;
  + margin-left: calc(#{rem(60px)} - #{$spacing-04} - #{$icon-size-01});
  }
  .#{$prefix}--btn--icon-only ::slotted([slot='icon']) {
  