Simplify border-related rules for like/unlike icons

We were keeping the same style and width when they were pressed, so we
can simply overwrite the color.

app/assets/stylesheets/in_favor_against.scss

@@ -41,7 +41,7 @@
       &:active,
       &[aria-pressed=true] {
         background: $like;
-        border: 2px solid $like;
+        border-color: $like;
       }
     }
   }
@@ -54,7 +54,7 @@
       &:active,
       &[aria-pressed=true] {
         background: $unlike;
-        border: 2px solid $unlike;
+        border-color: $unlike;
       }
     }
   }