fix(WKWebView Scrolling): fixed broken scroll (#372)

fixes #371

ios/RNCWKWebView.m

 {
   _scrollEnabled = scrollEnabled;
   _webView.scrollView.scrollEnabled = scrollEnabled;
-
-  // Override the scrollView delegate to prevent scrolling.
-  if (!scrollEnabled) {
-    _webView.scrollView.delegate = self;
-  } else {
-    _webView.scrollView.delegate = _webView;
-  }
 }
 
 - (void)scrollViewDidScroll:(UIScrollView *)scrollView
 {
   // Don't allow scrolling the scrollView.
-  scrollView.bounds = _webView.bounds;
+  if (!_scrollEnabled) {
+    scrollView.bounds = _webView.bounds;
+  }
 }
 
 - (void)setShowsHorizontalScrollIndicator:(BOOL)showsHorizontalScrollIndicator