Adding blog post for 9.3.4 patch release

https://add-9-3-3-blog-post.about.gitlab.com/2017/07/03/gitlab-9-dot-3-dot-3-released/

https://add-9-3-3-blog-post.about.gitlab.com/2017/07/04/gitlab-9-dot-3-dot-4-released/

Note: We decided not to announce 9.3.3 and rename the blog post to 9.3.4 instead. I've included a note about this in the blog post.