docs: fixing typo

subjects/java/checkpoints/good-bye-mars/README.md

@@ -1,14 +1,14 @@
-## GoodbyMars
+## GoodbyeMars
 
 ### Instructions
 
-In a file named `GoodbyMars.java` write a function `goodbyMars` that returns the string 'Good by Mars !'.
+In a file named `GoodbyeMars.java` write a function `goodbyeMars` that returns the string 'Good bye Mars !'.
 
 ### Expected Functions
 
 ```java
-public class GoodbyMars {
-    public static String goodbyMars() {
+public class GoodbyeMars {
+    public static String goodbyeMars() {
         // your code here
     }
 }
@@ -21,7 +21,7 @@ Here is a possible ExerciseRunner.java to test your function :
 ```java
 public class ExerciseRunner {
     public static void main(String[] args) {
-        System.out.println(GoodbyMars.goodbyMars());
+        System.out.println(GoodbyeMars.goodbyeMars());
     }
 }
 ```
@@ -31,6 +31,6 @@ and its output :
 ```shell
 $ javac *.java -d build
 $ java -cp build ExerciseRunner
-Good by Mars !
+Good bye Mars !
 $
 ```