docs: fixing files naming format

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

@@ -1,36 +0,0 @@
-## GoodbyMars
-
-### Instructions
-
-In a file named `GoodbyMars.java` write a function `goodbyMars` that returns the string 'Good by Mars !'.
-
-### Expected Functions
-
-```java
-public class GoodbyMars {
-    public static String goodbyMars() {
-        // your code here
-    }
-}
-```
-
-### Usage
-
-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());
-    }
-}
-```
-
-and its output :
-
-```shell
-$ javac *.java -d build
-$ java -cp build ExerciseRunner
-Good by Mars !
-$
-```

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

@@ -0,0 +1,36 @@
+## GoodbyeMars
+
+### Instructions
+
+In a file named `GoodbyeMars.java` write a function `goodbyeMars` that returns the string 'Good bye Mars !'.
+
+### Expected Functions
+
+```java
+public class GoodbyeMars {
+    public static String goodbyeMars() {
+        // your code here
+    }
+}
+```
+
+### Usage
+
+Here is a possible `ExerciseRunner.java` to test your function :
+
+```java
+public class ExerciseRunner {
+    public static void main(String[] args) {
+        System.out.println(GoodbyeMars.goodbyeMars());
+    }
+}
+```
+
+and its output :
+
+```shell
+$ javac *.java -d build
+$ java -cp build ExerciseRunner
+Good bye Mars !
+$
+```

subjects/java/checkpoints/system-logger/README.md

@@ -16,7 +16,7 @@ public class SystemLog {
 
 ### Usage
 
-Here is a possible ExerciseRunner.java to test your function :
+Here is a possible `ExerciseRunner.java` to test your function :
 
 ```java
 public class ExerciseRunner {

subjects/java/checkpoints/universal-greeting/README.md

@@ -22,7 +22,7 @@ public class UniversalGreeting {
 
 ### Usage
 
-Here is a possible ExerciseRunner.java to test your function :
+Here is a possible `ExerciseRunner.java` to test your function :
 
 ```java
 public class ExerciseRunner {