Add Section and Article to DefaultBlockRenderMap (#2212)

Summary:
*Before* submitting a pull request, please make sure the following is done...

1. Fork the repo and create your branch from `master`.
2. If you've added code that should be tested, add tests!
3. If you've changed APIs, update the documentation.
4. Ensure that:
  * The test suite passes (`npm test`)
  * Your code lints (`npm run lint`) and passes Flow (`npm run flow`)
  * You have followed the [testing guidelines](https://github.com/facebook/draft-js/wiki/Testing-for-Pull-Requests)
5. If you haven't already, complete the [CLA](https://code.facebook.com/cla).

Please use the simple form below as a guideline for describing your pull request.

Thanks for contributing to Draft.js!

-

**Summary**

Fixes #2074
Updated the default block render map to have the section and article tags.
Pull Request resolved: #2212

Reviewed By: claudiopro

Differential Revision: D18246366

Pulled By: mrkev

fbshipit-source-id: 144f7721d92d6efcbb5c969ba992841eb9bd5f15

src/model/constants/DraftBlockType.js

@@ -27,7 +27,9 @@ export type CoreDraftBlockType =
   | 'ordered-list-item'
   | 'blockquote'
   | 'code-block'
-  | 'atomic';
+  | 'atomic'
+  | 'section'
+  | 'article';
 
 /**
  * User defined types can be of any valid string.

src/model/immutable/DefaultDraftBlockRenderMap.js

@@ -47,6 +47,12 @@ const DefaultDraftBlockRenderMap: DefaultCoreDraftBlockRenderMap = Map({
   'header-six': {
     element: 'h6',
   },
+  section: {
+    element: 'section',
+  },
+  article: {
+    element: 'article',
+  },
   'unordered-list-item': {
     element: 'li',
     wrapper: UL_WRAP,