refactor: add final statement

Author: vbetsch

src/main/java/io/github/vbetsch/codecracker/CodeCracker.java

@@ -3,7 +3,7 @@
 import java.util.Map;
 
 public class CodeCracker {
-    Map<Character, Character> translations = Map.of(
+    final Map<Character, Character> translations = Map.of(
             'a', '!',
             'b', ')'
     );