Fix calling onScroll multiple times with incorrect y-axis offset (#144)

Author: tomekzaw

ios/MarkdownTextInputDecoratorView.mm

@@ -70,8 +70,10 @@ - (void)didMoveToWindow {
   } else if ([backedTextInputView isKindOfClass:[RCTUITextView class]]) {
     _textView = (RCTUITextView *)backedTextInputView;
     [_textView setMarkdownUtils:_markdownUtils];
-    object_setClass(_textView.layoutManager, [MarkdownLayoutManager class]);
-    [_textView.layoutManager setValue:_markdownUtils forKey:@"markdownUtils"];
+    NSLayoutManager *layoutManager = _textView.layoutManager; // switching to TextKit 1 compatibility mode
+    layoutManager.allowsNonContiguousLayout = NO; // workaround for onScroll issue
+    object_setClass(layoutManager, [MarkdownLayoutManager class]);
+    [layoutManager setValue:_markdownUtils forKey:@"markdownUtils"];
   } else {
     react_native_assert(false && "Cannot enable Markdown for this type of TextInput.");
   }