Bump gunicorn from 19.3.0 to 19.5.0 in /requirements

Bumps [gunicorn](https://github.com/benoitc/gunicorn) from 19.3.0 to 19.5.0.
- [Release notes](https://github.com/benoitc/gunicorn/releases)
- [Commits](https://github.com/benoitc/gunicorn/compare/19.3...19.5.0)

Signed-off-by: dependabot[bot] <support@github.com>

requirements/requirements.txt

@@ -9,7 +9,7 @@ django-localflavor==1.1
 Django==1.7.10
 easy-thumbnails==2.2
 eav-django==1.4.7
-gunicorn==19.3.0
+gunicorn==19.5.0
 html5lib==0.9999999
 Pillow==2.9.0
 pisa==3.0.33