enclose boolean with string in docker-compose env

deployments/examples/ocis_traefik/docker-compose.yml

@@ -58,7 +58,7 @@ services:
       PROXY_TLS: "false" # do not use SSL between Traefik and oCIS
       # INSECURE: needed if oCIS / Traefik is using self generated certificates
       OCIS_INSECURE: "${INSECURE:-false}"
-      GRAPH_LDAP_INSECURE: true # https://github.com/owncloud/ocis/issues/3812
+      GRAPH_LDAP_INSECURE: "true" # https://github.com/owncloud/ocis/issues/3812
       # basic auth (not recommended, but needed for eg. WebDav clients that do not support OpenID Connect)
       PROXY_ENABLE_BASIC_AUTH: "${PROXY_ENABLE_BASIC_AUTH:-false}"
       # admin user password
@@ -84,6 +84,5 @@ volumes:
   ocis-config:
   ocis-data:
 
-
 networks:
   ocis-net: