make DocumentFragment type have the real type name

Author: SimenB

packages/pretty-format/src/plugins/dom_element.js

@@ -37,7 +37,7 @@ type Comment = {
   data: string,
   nodeType: 8,
 };
-type Fragment = {
+type DocumentFragment = {
   children: Array<Element>,
   nodeType: 11,
 };
@@ -69,7 +69,7 @@ const propsReducer = (props, attribute) => {
 };
 
 export const serialize = (
-  node: Element | Text | Comment | Fragment,
+  node: Element | Text | Comment | DocumentFragment,
   config: Config,
   indentation: string,
   depth: number,