use conditional mixin for transitions on buttons

scss/_buttons.scss

@@ -18,7 +18,7 @@
   user-select: none;
   border: $border-width solid transparent;
   @include button-size($btn-padding-y, $btn-padding-x, $font-size-base, $line-height, $btn-border-radius);
-  transition: all .2s ease-in-out;
+  @include transition(all .2s ease-in-out);
 
   &,
   &:active,