Upgrade uwsgi to 2.0.17.1 to (hopefully) fix compilation errors on Heroku

ref: #220, https://github.com/unbit/uwsgi/issues/1468

requirements/production.txt

@@ -1,7 +1,7 @@
 -r base.txt
 # Additional dependencies for Heroku deployment
 dj-database-url==0.4.1
-uwsgi==2.0.14
+uwsgi==2.0.17.1
 psycopg2==2.7.3.1
 whitenoise==3.2.2
 boto==2.45.0