Add NO_CONTRACTS to environment

As outlined in alphagov/govuk-developer-docs@4b624a7
this is a recommended setting when running the app. I also had problems
running the app without it.

Author: pezholio

projects/govuk-developer-docs/docker-compose.yml

@@ -17,6 +17,7 @@ services:
     <<: *govuk-developer-docs
     environment:
       LANG: "C.UTF-8"
+      NO_CONTRACTS: true
 
   govuk-developer-docs-app:
     <<: *govuk-developer-docs