Fix trusted url on docker-compose.yml.

docker-compose.yml

@@ -54,7 +54,7 @@ services:
       # and allows all iframing etc. See wekan/server/policy.js
       - BROWSER_POLICY_ENABLED=true
       # When browser policy is enabled, HTML code at this Trusted URL can have iframe that embeds Wekan inside.
-      - TRUSTED_URL=
+      - TRUSTED_URL=''
     depends_on:
       - wekandb