return the correct value from interpret

Author: froydnj

lib/message_format/interpreter.rb

@@ -48,10 +48,11 @@ def initialize ( message, missing_params )
 
     def interpret ( elements )
       @missing_ids = []
-      interpret_subs(elements)
+      interpreted = interpret_subs(elements)
       if @raise_on_missing_params && !@missing_ids.empty?
         raise MissingParametersError.new('Missing parameters detected during interpretation', @missing_ids.compact)
       end
+      interpreted
     end
 
     def interpret_subs ( elements, parent=nil )