Update AppVersion badge in README

Updated AppVersion badge in README.md from 1.3.2 to 2.1.5.

Author: serut

charts/stirling-pdf/README.md

@@ -1,6 +1,6 @@
 # stirling-pdf-chart
 
-![Version: 2.2.0](https://img.shields.io/badge/Version-2.2.0-informational?style=flat-square) ![AppVersion: 1.3.2](https://img.shields.io/badge/AppVersion-1.3.2-informational?style=flat-square)
+![Version: 2.2.0](https://img.shields.io/badge/Version-2.2.0-informational?style=flat-square) ![AppVersion: 2.1.5](https://img.shields.io/badge/AppVersion-2.1.5-informational?style=flat-square)
 
 locally hosted web application that allows you to perform various operations on PDF files