Bump gunicorn from 18.0 to 19.5.0

Bumps [gunicorn](https://github.com/benoitc/gunicorn) from 18.0 to 19.5.0.
- [Release notes](https://github.com/benoitc/gunicorn/releases)
- [Commits](benoitc/gunicorn@18.0...19.5.0)

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

Author: dependabot[bot]

requirements.txt

@@ -3,7 +3,7 @@ Pygments==1.6
 beautifulsoup4==4.3.2
 blinker==1.3
 docutils==0.11
-gunicorn==18.0
+gunicorn==19.5.0
 itsdangerous==0.23
 newrelic==2.34.0.29
 pyephem==3.7.5.3