Suggest editing H1 in header.php

If header.php called out with single.php or page.php, it will create duplicated H1 for current page.
Update header.php H1 with function is_singular()

Update header.php H1 with function is_singular() is work as expected.
When current page as a Post, Page, or Attachment the header H1 has turn to div. H1 has normally appear in Blog or Category page.
Merge pull request #1 from ReeZh/master

Editing H1 in header.php