Fix: can't drag to the end of track on iOS (#334)

* Check if targeted value exceeds the range
* Cover the check with comment explaining its purpose

Author: BartoszKlonowski

src/ios/RNCSliderManager.m

@@ -77,9 +77,14 @@ - (void)tapHandler:(UITapGestureRecognizer *)gesture {
 }
 
 static float discreteValue(RNCSlider *sender, float value) {
+  // Check if thumb should reach the maximum value and put it on the end of track if yes.
+  // To avoid affecting the thumb when on maximum, the `step >= (value - maximum)` is not checked.
+  if (sender.step > 0 && value >= sender.maximumValue) {
+    return sender.maximumValue;
+  }
+
   // If step is set and less than or equal to difference between max and min values,
   // pick the closest discrete multiple of step to return.
-
   if (sender.step > 0 && sender.step <= (sender.maximumValue - sender.minimumValue)) {
 
     // Round up when increase, round down when decrease.