chore: fixed a spacing issue and found reason for

gradle build fails

Author: haldanek

lesson_13/maps_java/maps_app/build.gradle.kts

@@ -32,7 +32,7 @@ dependencies {
 
 application {
     // Define the main class for the application.
-    mainClass.set("com.codedifferently.lesson12.Lesson12")
+    mainClass.set("com.codedifferently.lesson13.Lesson13")
 }
 
 tasks.named<Test>("test") {

lesson_13/maps_java/maps_app/src/main/java/com/codedifferently/lesson13/Lesson13.java

@@ -11,7 +11,7 @@ public class Lesson13 {
   public int findPermutationDifference(String s, String t) {
     HashMap<Character, Integer> indexMap = new HashMap<>();
 
-    for (int i =0; i < s.length(); i++) {
+    for (int i = 0; i < s.length(); i++) {
       indexMap.put(s.charAt(i), i);
     }