Fix accessibility label default props (peacechen#128).

Change scrollViewAccessibilityLabel and cancelButtonAccessibilityLabel defaults to empty strings `""`.

Author: peacechen

index.js

@@ -115,8 +115,8 @@ const defaultProps = {
     listItemAccessible:             false,
     cancelButtonAccessible:         false,
     scrollViewAccessible:           false,
-    scrollViewAccessibilityLabel:   undefined,
-    cancelButtonAccessibilityLabel: undefined,
+    scrollViewAccessibilityLabel:   "",
+    cancelButtonAccessibilityLabel: "",
     passThruProps:                  {},
     selectTextPassThruProps:        {},
     optionTextPassThruProps:        {},