Use a more expressive method of rewriting values

This achieves almost the same, except that this version doesn't change
the original value. If that's really desired, `transform_values!` can be
used. It makes it clearer what's going on.

lib/puppet/type/rabbitmq_parameter.rb

@@ -106,9 +106,6 @@ def validate_value(value)
   def munge_value(value)
     return value if value(:autoconvert) == :false
 
-    value.each do |k, v|
-      value[k] = v.to_i if v =~ %r{\A[-+]?[0-9]+\z}
-    end
-    value
+    value.transform_values { |v| v =~ %r{\A[-+]?[0-9]+\z} ? v.to_i : v }
   end
 end