Merge branch 'fix-defined-classes'

etl/src/main/java/Etl.java

@@ -1,2 +1,2 @@
-public Etl {
+public class Etl {
 }

nucleotide-count/src/main/java/DNA.java

@@ -1,2 +1,2 @@
-public DNA {
+public class DNA {
 }

word-count/src/main/java/WordCount.java

@@ -1,2 +1,2 @@
-public WordCount {
+public class WordCount {
 }