plugin: Added .params.configuration to init call

This tells the plugin both the `lightning-dir` as well as the
`rpc-filename` to use to talk to `lightningd`. Prior to this they'd
had to guess.

Signed-off-by: Christian Decker <decker.christian@gmail.com>

contrib/plugins/helloworld.py

@@ -45,7 +45,7 @@ def json_getmanifest(request):
     }
 
 
-def json_init(request, options):
+def json_init(request, options, configuration):
     """The main daemon is telling us the relevant cli options
     """
     global greeting