Only use 2 workers to avoid hitting pool limits
Only use 2 workers to avoid hitting pool limits

SQLAlchemy has a default connection pool size of 5, and with four workers this
will use the default 20 connections that Heroku's low-end PG databases allow.
Hopefully notching this down to 2 will avoid the problems we're having with DB
connectivity.

openannotation/annotateit,openannotation/annotateit