Have "Edit on GitHub" point to master instead of gh-pages

Summary:
If someone clicks on `Edit on GitHub` to edit a doc for a pull request, for example,
then we should point to `master` instead of `gh-pages`.

> Also fixed some Windows-based line endings. From CRLF to LF.

Test Plan: https://www.facebook.com/pxlcld/pvV2

Reviewers: IslamAbdelRahman, lgalanis, sdong

Reviewed By: sdong

Subscribers: andrewkr, dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D63435

docs/_includes/doc.html

@@ -18,7 +18,7 @@
     {% else %}
       {{ content }}
 
-      <p><a class="edit-page-link" href="https://github.com/{{ site.ghrepo }}/tree/gh-pages/{{ page.path }}" target="_blank">Edit on GitHub</a></p>
+      <p><a class="edit-page-link" href="https://github.com/{{ site.ghrepo }}/blob/master/docs/{{ page.path }}" target="_blank">Edit on GitHub</a></p>
     {% endif %}
   </article>
   {% include doc_paging.html %}