bugfix setter of light.saturation and light.brightness

Hi, thank you for a great gem.

I have found a bug and fixed it.

### bug
following code sets random values to hue, but `saturation` and `brightness` are not worked.
```ruby
require 'hue'

hue = Hue::Client.new
hue.lights.each do |light|
  light.on = true
end

loop do
  hue.lights.each do |light|
    puts light.name
    light.hue = rand 65535
    light.saturation = rand 255  ## not work
    light.brightness = rand 255  ## not work
  end
  sleep 0.1
end
```

they got error messages from hue bridge.
```
"[{\"error\":{\"type\":6,\"address\":\"/lights/1/state/brightness\",\"description\":\"parameter, brightness, not available\"}}]"
"[{\"error\":{\"type\":6,\"address\":\"/lights/2/state/saturation\",\"description\":\"parameter, saturation, not available\"}}]"
```

### fixed
use `STATE_KEYS_MAP` instead of `KEYS_MAP` in translate_keys function.