Comment secret key base on production enviroments

Although our installer automatically generates a secret key base, we
want to avoid any chance of installations who don't use the installer
having an empty secret key base or using the default secret key base we
provide to use on development and test environments.

config/secrets.yml.example

@@ -1,7 +1,3 @@
-default: &default
-  secret_key_base: 56792feef405a59b18ea7db57b4777e855103882b926413d4afdfb8c0ea8aa86ea6649da4e729c5f5ae324c0ab9338f789174cf48c544173bc18fdc3b14262e4
-  email_interceptor_recipients: ""
-
 maps: &maps
   map_tiles_provider: "//{s}.tile.openstreetmap.org/{z}/{x}/{y}.png"
   map_tiles_provider_attribution: "&copy; <a href=\"http://osm.org/copyright\">OpenStreetMap</a> contributors"
@@ -22,15 +18,15 @@ http_basic_auth: &http_basic_auth
 development:
   http_basic_username: "dev"
   http_basic_password: "pass"
-  <<: *default
+  secret_key_base: 56792feef405a59b18ea7db57b4777e855103882b926413d4afdfb8c0ea8aa86ea6649da4e729c5f5ae324c0ab9338f789174cf48c544173bc18fdc3b14262e4
   <<: *maps
 
 test:
-  <<: *default
+  secret_key_base: 56792feef405a59b18ea7db57b4777e855103882b926413d4afdfb8c0ea8aa86ea6649da4e729c5f5ae324c0ab9338f789174cf48c544173bc18fdc3b14262e4
   <<: *maps
 
 staging:
-  secret_key_base: ""
+  # secret_key_base: ""
   server_name: ""
   # mailer_delivery_method: :smtp
   # smtp_settings:
@@ -43,6 +39,7 @@ staging:
   #   :enable_starttls_auto: true
   force_ssl: true
   delay_jobs: true
+  email_interceptor_recipients: ""
   errbit_host: ""
   errbit_project_key: ""
   errbit_project_id: 1
@@ -52,12 +49,11 @@ staging:
   http_basic_password: ""
   managers_url: ""
   managers_application_key: ""
-  <<: *default
   <<: *maps
   <<: *apis
 
 preproduction:
-  secret_key_base: ""
+  # secret_key_base: ""
   server_name: ""
   # mailer_delivery_method: :smtp
   # smtp_settings:
@@ -70,6 +66,7 @@ preproduction:
   #   :enable_starttls_auto: true
   force_ssl: true
   delay_jobs: true
+  email_interceptor_recipients: ""
   errbit_host: ""
   errbit_project_key: ""
   errbit_project_id: 1
@@ -89,7 +86,7 @@ preproduction:
   <<: *apis
 
 production:
-  secret_key_base: ""
+  # secret_key_base: ""
   server_name: ""
   # mailer_delivery_method: :smtp
   # smtp_settings: