docs: Update Maven badge URL

Author: SMadani

README.md

@@ -1,6 +1,6 @@
 # Vonage Server SDK for Kotlin (JVM)
 
-[![Maven Release](https://maven-badges.herokuapp.com/maven-central/com.vonage/server-sdk-kotlin/badge.svg)](https://central.sonatype.com/artifact/com.vonage/server-sdk-kotlin)
+[![Maven Central](https://img.shields.io/maven-central/v/com.vonage/server-sdk-kotlin)](https://central.sonatype.com/artifact/com.vonage/server-sdk-kotlin)
 [![Build Status](https://github.com/Vonage/vonage-kotlin-sdk/actions/workflows/build.yml/badge.svg)](https://github.com/Vonage/vonage-kotlin-sdk/actions/workflows/build.yml)
 [![codecov](https://codecov.io/gh/Vonage/vonage-kotlin-sdk/graph/badge.svg?token=YNBJUD8OUT)](https://codecov.io/gh/Vonage/vonage-kotlin-sdk)
 ![SLOC](https://sloc.xyz/github/Vonage/vonage-kotlin-sdk)