Update ReverseNumber (#4257)

- removes an unused import,
- fixes the order of the of the _modifiers_ in the definition of the class `ReverseNumber`.

src/main/java/com/thealgorithms/maths/ReverseNumber.java

@@ -1,11 +1,9 @@
 package com.thealgorithms.maths;
 
-import java.lang.IllegalArgumentException;
-
 /**
  * @brief utility class reversing numbers
  */
-final public class ReverseNumber {
+public final class ReverseNumber {
     private ReverseNumber() {
     }