Remove details normalization, update summary requirement (sindres…

…orhus#21)

* Remove normalization for the `details` element

Firefox supports `details` since version 49, and Edge is not supported by modern-normalize.

* Update normalization requirement for the `summary` element

Support for the `summary` element with `display: list-item` was added to Firefox in version 49.

modern-normalize.css

@@ -275,15 +275,7 @@ progress {
  ========================================================================== */
 
 /*
- * Add the correct display in Edge and Firefox.
- */
-
-details {
- display: block;
-}
-
-/*
- * Add the correct display in all browsers.
+ * Add the correct display in Chrome and Safari.
  */
 
 summary {