Re add ios tap handler (#201)

* Revert "Fix touch to seek flicker on iOS (#136)"

This reverts commit 71315cb.

* fix(ios): tap to slide scales values correctly

Also updates the example to listen to onSlidingComplete so the
tap events are handled well

example/SliderExample.js

@@ -31,6 +31,7 @@ class SliderExample extends React.Component<$FlowFixMeProps, $FlowFixMeState> {
         <Slider
           {...this.props}
           onValueChange={value => this.setState({value: value})}
+          onSlidingComplete={value => this.setState({value: value})}
         />
       </View>
     );

src/ios/RNCSlider.m

@@ -10,11 +10,25 @@
 @implementation RNCSlider
 {
   float _unclippedValue;
+  UITapGestureRecognizer * tapGesturer;
 }
 
 - (instancetype)initWithFrame:(CGRect)frame
 {
-    return [super initWithFrame:frame];
+    self = [super initWithFrame:frame];
+    if (self) {
+        tapGesturer = [[UITapGestureRecognizer alloc] initWithTarget: self action:@selector(tapHandler:)];
+        [tapGesturer setNumberOfTapsRequired: 1];
+        [self addGestureRecognizer:tapGesturer];
+    }
+    return self;
+}
+
+- (void)tapHandler:(UITapGestureRecognizer *)gesture {
+    CGPoint touchPoint = [gesture locationInView:self];
+    float rangeWidth = self.maximumValue - self.minimumValue;
+    float sliderPercent = touchPoint.x / self.bounds.size.width;
+    [self setValue:self.minimumValue + (rangeWidth * sliderPercent) animated: YES];
 }
 
 - (void)setValue:(float)value