Upgrade nginx ansible role

Upgraded to allow gzipping of our javascript assets.  Other changes
include turning off server tokens and installing the full nginx package
which includes additional modules which are not utilized by the app.

deployment/ansible/roles.yml

@@ -7,7 +7,7 @@
 - src: azavea.git
   version: 0.1.0
 - src: azavea.nginx
-  version: 0.2.1
+  version: 0.3.1
 - src: azavea.daemontools
   version: 0.1.0
 - src: azavea.postgresql-support