Update readme for 100.2.1

Author: dg0yal

README.md

@@ -20,7 +20,7 @@ The ```master``` branch of this repository contains samples configured for the l
 * Scenes - Display scenes, 3D symbols, and scene layers
 
 ## Requirements
-* [ArcGIS Runtime SDK for iOS](https://developers.arcgis.com/en/ios/) 100.2 (or higher). 
+* [ArcGIS Runtime SDK for iOS](https://developers.arcgis.com/en/ios/) 100.2.1 (or higher). 
 * XCode 9 (or higher)
 * iOS 11 SDK (or higher)