Closes #157 - use javadoc.io badge in README

Author: ascopes

README.md

@@ -1,6 +1,6 @@
 ![Java 11+](https://img.shields.io/badge/Java-11+-yellow?logo=openjdk)
 [![Build Status](https://github.com/ascopes/java-compiler-testing/actions/workflows/build.yml/badge.svg?branch=main)](https://github.com/ascopes/java-compiler-testing/actions/workflows/build.yml)
-[![JavaDoc](https://img.shields.io/badge/JavaDoc-Latest-red)](https://ascopes.github.io/java-compiler-testing)
+[![javadoc](https://javadoc.io/badge2/io.github.ascopes.jct/java-compiler-testing/javadoc.svg)](https://javadoc.io/doc/io.github.ascopes.jct/java-compiler-testing)
 [![Code Coverage](https://codecov.io/gh/ascopes/java-compiler-testing/branch/main/graph/badge.svg?token=VT74BP2742)](https://codecov.io/gh/ascopes/java-compiler-testing)
 [![Maven Central](https://img.shields.io/maven-central/v/io.github.ascopes.jct/java-compiler-testing)](https://repo1.maven.org/maven2/io/github/ascopes/jct/java-compiler-testing)
 [![Issues](https://img.shields.io/github/issues-raw/ascopes/java-compiler-testing?color=orange)](https://github.com/ascopes/java-compiler-testing/issues)