Add a mutation for kwargs

[dkubb]

When using mutant on some code that uses kwargs, it came up with only one alive mutation:

-def initialize(name, includes:, **options)
+def initialize(name__mutant__, includes:, **options)
   super
 end

Now obviously I can kill this one by renaming name to _name, but I noticed there were no mutations for includes to includes__mutant nor for **options to **options__mutant__. I think both of these should be added to make sure these options are being handled.