fix: floation point rounding issue

Change `getValueFromPosition` value calculation.
The `+ this.min` needs to be outside, otherwise it gets the wrong
answer unless `this.min` is divisible by this.step.
Big ups to @jpmckinney

Closes issue #50, #91
Merge pull request #95 from andreruffert/fix-floating-point-rounding-issue

fix: floation point rounding issue