fix the reading of the env variables in the config

Author: stuzart

docker/virtuoso_settings.docker.yml

@@ -5,7 +5,7 @@ production:
   username: dba
   password: <%= ENV["DBA_PASSWORD"] %>
 
-  private_graph: ENV["RDF_PRIVATE_GRAPH"]
-  public_graph: ENV["RDF_PUBLIC_GRAPH"]
+  private_graph: <%= ENV["RDF_PRIVATE_GRAPH"] %>
+  public_graph: <%= ENV["RDF_PUBLIC_GRAPH"] %>
 
   disabled: <%= !ENV["VIRTUOSO"].present? %>