Update ARIA attributes on ranges

[aitchiss]

Fixes #171

In the Hue component:

• aria-valuetext has been changed to aria-valuenow. Since the "human understandable" value is numeric, we don't need both valuetext and valuenow, and valuenow is the "required" attribute
• aria-valuemin has been set to 0 and aria-valuemax has been set to 360 to provide a bit more context for screen reader users

In the Alpha component:

• aria-valuenow has been added. This is in addition to aria-valuetext. Screen readers will generally read out the more understandable valuetext, but valuenow is a required attribute to accompany it
• aria-valuemin has been set to 0 and aria-valuemax has been set to 100

In the Saturation component:

No change has been made! I don't believe there is an available numeric representation of the current value, so in this case I believe we can omit aria-valuenow for the time being until #152 is addressed.

Snapshot tests have been updated to reflect the new attributes 🙂

Check out the docs for aria-valuenow for more context

[omgovich]

Oh, wow! Thanks a lot for this contribution! I'll check it as far as I can!

[omgovich]

Tested it locally with VoiveOver and added a simple test for that. Everything works well.
Thanks again!

[aitchiss]

Thank you @omgovich!

[smellai]

@aitchiss thanks for this improvement!
@omgovich looks like the demo in the homepage is not updated yet with this change?

Looking forward the fix for #152 too