fixed more typos

exercise3/Exercise3.java

@@ -27,7 +27,7 @@ class Crow extends Bird {
 }
 
 public class Exercise3 {
-    public Teht3() {
+    public Exercise3() {
         System.out.println("Exercise 3");
 
         challenge1(new Crow());

exercise4/Exercise4.java

 package fi.utu.tech.ooj.exercise4.exercise4;
 
 public class Exercise4 {
-    public Teht4() {
+    public Exercise4() {
         System.out.println("Exercise 4");
     }
 }