fix readme badge

Author: andrewparmet

README.md

@@ -1,7 +1,7 @@
 # protokt 
 
 [![CircleCI](https://circleci.com/gh/open-toast/protokt.svg?style=svg)](https://circleci.com/gh/open-toast/protokt)
-[![Maven Central](https://img.shields.io/maven-central/v/com.toasttab.protokt/protokt-runtime)](https://search.maven.org/artifact/com.toasttab.protokt/protokt-codegen)
+[![Maven Central](https://img.shields.io/maven-central/v/com.toasttab.protokt/protokt-runtime)](https://search.maven.org/artifact/com.toasttab.protokt/protokt-runtime)
 [![Gradle Portal](https://img.shields.io/maven-metadata/v/https/plugins.gradle.org/m2/com/toasttab/protokt/protokt-gradle-plugin/maven-metadata.xml.svg?label=gradle-portal&color=yellowgreen)](https://plugins.gradle.org/plugin/com.toasttab.protokt)
 
 Protocol Buffer compiler and runtime for Kotlin.