Fixed typos

Main.java

@@ -9,9 +9,9 @@ public class Main {
     public static void main(String[] args) throws Exception {
         System.out.println("Advanced Course in Object-Oriented Programming, Part 4 Exercises");
 
-        new Teht1();
-        new Teht2();
-        new Teht3();
-        new Teht4();
+        new Exercise1();
+        new Exercise2();
+        new Exercise3();
+        new Exercise4();
     }
 }

Exercise3/Exercise3.java → exercise3/Exercise3.java

@@ -26,7 +26,7 @@ class Crow extends Bird {
     }
 }
 
-public class Teht3 {
+public class Exercise3 {
     public Teht3() {
         System.out.println("Exercise 3");
 

Exercise4/Exercise4.java → exercise4/Exercise4.java

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