[Slider] Fix Slider div style

[tintin1343]

• PR has tests / docs demo, and is linted.
• Commit and PR titles begin with [ComponentName], and are in imperative form: "[Component] Fix leaky abstraction".
• Description explains the issue / use-case resolved, and auto-closes the related issue(s) (http://tr.im/vFqem).

Resolves: #3282

The issue with the current slider style was that it used to apply styles twice because of the prepareStyles including style and hence the width % was being applied twice.

I removed the style parameter in object.assign as that was the reason of including the styles twice.
So the style will be applied only once to the Slider div. Renamed styles.root to style.slider

[oliviertassinari]

This PR is introducing a breaking change. Do we want to wait for v0.16?
Or we could consider that the behavior was already broken end it's not a breaking change.

[tintin1343]

I don't mind anything here. I would like @nathanmarks and @mbrookes to comment.

[mbrookes]

@oliviertassinari - I agree with you that this is a bug, but potentially a breaking change to remove style from slider. How useful might it be to be able to style the slider at this level rather than the root div? (i.e. how likely is it someone is depending on the style prop being removed here?)

[oliviertassinari]

Object.assign is no longer useful.

[oliviertassinari]

how likely is it someone is depending on the style prop being removed here?

I would say the probability is low and I would consider this a bug before all.

@tintin1343 Could you have a look at my comment? It would be good to merge this PR before releasing v0.15.0.

[tintin1343]

@oliviertassinari : Sorry for the delay, was out of action for a couple days. I will get back to you on this.

[tintin1343]

@oliviertassinari : I remove Object.assign() . Do Check it.

[oliviertassinari]

@tintin1343 That looks good to me. Could you squash?

[tintin1343]

@oliviertassinari : Done.

[sghall]

Well, I was depending on the style prop for the Slider. Why is the default bottom margin 48px? That's seems ridiculously large, that's all I was trying to change. Great work project BTW!

[oliviertassinari]

Why is the default bottom margin 48px?

I would even go further. Why do we have a default margin?

Well, I was depending on the style prop for the Slider.

We have many customization points on the others components. You could submit a PR to add a sliderStyle property.