Bump gunicorn from 19.3.0 to 19.5.0

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

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

requirements.txt

@@ -13,7 +13,7 @@ beautifulsoup4==4.3.2
 blinker==1.3
 cssmin==0.2.0
 futures==3.0.2
-gunicorn==19.3.0
+gunicorn==19.5.0
 itsdangerous==0.24
 jsmin==2.1.1
 numpy==1.9.2