Update dependency org.apache.maven.plugins:maven-source-plugin to v3 (#22)

Co-authored-by: Renovate Bot <[email protected]>

Author: renovate[bot]

pom.xml

@@ -41,7 +41,7 @@
         <spotless-plugin.version>2.0.3</spotless-plugin.version>
         <google-java-format.version>1.7</google-java-format.version>
         <compiler-plugin.version>3.8.1</compiler-plugin.version>
-        <source-plugin.version>2.4</source-plugin.version>
+        <source-plugin.version>3.2.1</source-plugin.version>
         <javadoc-plugin.version>3.2.0</javadoc-plugin.version>
         <gpg-plugin.version>1.6</gpg-plugin.version>
         <versions-plugin.version>2.8.1</versions-plugin.version>