fix(slider): increment the value properly when step is a decimal number

[kennethcachia]

Closes #2015

[Kiougar]

You should use return Math.round(formattedValue * 1000) / 1000. It's faster.
JSperf: http://jsperf.com/math-round-vs-tofixed2/5

[kennethcachia]

Thanks @Kiougar! Pushed an update.

[mprentic-harris]

It's not clear to me that this resolves the issue. Previously Math.round(value / step) * step was returning 14.700000000000001 or some such value. With this fix it will now return 14.700 or 14.7? Is this really addressing the cause of Math.round(0.15 / 0.05) * 0.05 equalling 0.15000000000000002? What if I have step="0.0001"?

[kennethcachia]

Hey @mprentic-harris!
It should return 14.7 and addresses #2015.