Refactor payment auth button to fit into table row

This looks a bit more cohesive with the rest of the row cells while
still standing out from the rest.

app/assets/stylesheets/darkswarm/ui.scss

@@ -61,6 +61,13 @@
   @include border-radius(0.5em);
 
   outline: none;
+
+  &.x-small {
+    padding: 0.5rem 0.75rem;
+    font-size: $text-xs;
+    font-weight: 600;
+    margin: 0;
+  }
 }
 
 .button.primary, button.primary {

app/views/spree/users/_transactions.html.haml

@@ -18,7 +18,7 @@
                   = payment.updated_at.strftime("%Y-%m-%d")
                 %td.order3
                   %a{ href: "#{payment.cvv_response_message}" }
-                    %button.bright
+                    %button.x-small
                       Authorize
                 %td.order5
                   = payment.display_amount