Avoid [ActiveSupport::OrderedOptions#dig]

The implementation has been updated upstream[^1] to expect symbolized
keys. MRSK relies heavily on the fact that nested keys are strings, so
we're removing existing uses of `#dig`.

[^1]: 5c15b586aa

lib/mrsk/commands/traefik.rb

@@ -55,7 +55,7 @@ class Mrsk::Commands::Traefik < Mrsk::Commands::Base
 
   private
     def cmd_option_args
-      if args = config.raw_config.dig(:traefik, "args")
+      if args = config.traefik["args"]
         optionize args
       else
         []
@@ -63,6 +63,6 @@ class Mrsk::Commands::Traefik < Mrsk::Commands::Base
     end
 
     def host_port
-      config.raw_config.dig(:traefik, "host_port") || CONTAINER_PORT
+      config.traefik["host_port"] || CONTAINER_PORT
     end
 end