Pagination move `.page-link:focus` outline value to variable...

Pagination move `.page-link:focus` outline value to variable `$pagination-focus-outline` so we can unset it via Sass and don't have to re-implement browser defaults

scss/_pagination.scss

@@ -24,7 +24,7 @@
 
   &:focus {
     z-index: 2;
-    outline: 0;
+    outline: $pagination-focus-outline;
     box-shadow: $pagination-focus-box-shadow;
   }
 

scss/_variables.scss

@@ -663,6 +663,7 @@ $pagination-border-width:           $border-width !default;
 $pagination-border-color:           $gray-300 !default;
 
 $pagination-focus-box-shadow:       $input-btn-focus-box-shadow !default;
+$pagination-focus-outline:          0 !default;
 
 $pagination-hover-color:            $link-hover-color !default;
 $pagination-hover-bg:               $gray-200 !default;