[hotfix] gunicorn version 19.4.? has issues serving static files

setup.py

@@ -103,7 +103,7 @@ def run(self):
         'flask-cache>=0.13.1, <0.14',
         'flask-login==0.2.11',
         'future>=0.15.0, <0.16',
-        'gunicorn>=19.3.0, <20.0',
+        'gunicorn>=19.3.0, <19.4.0',  # 19.4.? seemed to have issues
         'jinja2>=2.7.3, <3.0',
         'markdown>=2.5.2, <3.0',
         'pandas>=0.15.2, <1.0.0',