I want to automate the task of adding vedor prefixes using sass

In an attempt to do so I have tried this out:

@mixin bsupport($property: $value) { 
   -webkit-$property: $value;
   -moz-$property: $value;
   -ms-$property: $value;
   $property: $value;
}

body {
   @include bsupport(border-radius: 2px);
}

But it's not working.