Make the app good for Heroku

Procfile

@@ -1 +1 @@
-web: elixir -pa _build/prod/consolidated -S mix phoenix.server --no-halt
+web: mix phoenix.server --no-halt

config/prod.exs

@@ -1,27 +1,14 @@
 use Mix.Config
 
-# For production, we configure the host to read the PORT
-# from the system environment. Therefore, you will need
-# to set PORT=80 before running your server.
-#
-# You should also configure the url host to something
-# meaningful, we use this information when generating URLs.
-#
-# Finally, we also include the path to a manifest
-# containing the digested version of static files. This
-# manifest is generated by the mix phoenix.digest task
-# which you typically run after static files are built.
+config :logger, level: :info
+
 config :callum, Callum.Endpoint,
   http: [port: {:system, "PORT"}],
   url: [host: "example.com", port: 80],
   cache_static_manifest: "priv/static/manifest.json",
   secret_key_base: System.get_env("SECRET_KEY_BASE")
 
-# Do not print debug messages in production
-config :logger, level: :info
-
-# Configure your database
 config :callum, Callum.Repo,
   adapter: Ecto.Adapters.Postgres,
   url: {:system, "DATABASE_URL"},
-  pool_size: 20
+  pool_size: 10