Fix for blog cover image.

Signed-off-by: David Carlos <ddavidcarlos1392@gmail.com>
Signed-off-by: Marcos Ramos <ms.ramos@outlook.com>
Merge branch 'blog-picture-t' of https://github.com/fga-unb/noosfero into blog-picture-t

Conflicts:
	test/unit/blog_test.rb