fix issue that fail to publish gradle plugin to maven central

dependency-check-gradle/conf/publish/maven.gradle

@@ -66,6 +66,11 @@ task javadocJar(type: Jar) {
     from javadoc
 }
 
+task sourcesJar(type: Jar, dependsOn: classes) {
+    classifier = 'sources'
+    from sourceSets.main.allSource
+}
+
 artifacts {
     archives javadocJar, sourcesJar
 }