fix slider jumps to first value if value is not in stepsArray

[DominikFG]

As I used the slider with a stepsArray and an input to change the value, I found that if a value is entered in the input that's not in the stepsArray the slider jumps to its minimum value.

I changed it so that it jumps to the next higher value instead.

[codecov-io]

Codecov Report

Merging #626 into master will not change coverage. The diff coverage is 100%.

@@          Coverage Diff          @@
##           master   #626   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files           1      1           
  Lines         950    951    +1     
=====================================
+ Hits          950    951    +1

Impacted Files	Coverage Δ
src/rzslider.js	100% <100%> (ø)	:arrow_up:

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[evestraw]

I also run into this issue when the ceil is not in the step interval the ceil could be overshot.

[ViieeS]

I think we just need to respect enforceStep: false option when using stepsArray. This is old bug #410.