Mixing Hash and keyword arguments raises an error

Hello,

There's a bug with JRuby 9000 when defining a method that mixes a Hash argument with a keyword argument:

``` ruby
>> def foo(bar = {}, baz: nil)
 | end
=> :foo
>> foo({ "foo" => "bar" })
=> ArgumentError: unknown keyword: foo
```

This is not a problem with MRI.

Have a nice day!
