Freshly fetched "etl" compiles without error.

(contributes to #53)

etl/src/main/java/Etl.java

+import java.util.List;
+import java.util.Map;
+
 public class Etl {
+   public Map<String, Integer> transform(Map<Integer, List<String>> old) {
+      return null;
+   }
 }