This is just a small yaml formatting issue.
The modules property should be an array. There are two ways you can indicate an array in a widget: the yaml array, or with widget expressions.
The yaml format for an array does, as you have done, start the array element with a -. but that array element has to be on a new line indented from the name of the array object. So:
modules:
- hue-slider
The expression format just allows you to define a javascript array which is comma separated values between square brackets:
modules: =['hue-slider']