reverted change

Author: ghost

src/main/java/com/thealgorithms/ciphers/ProductCipher.java

@@ -25,13 +25,13 @@ public static void main(String[] args) {
             System.out.println(substitutionOutput);
 
             // Transposition encryption
-            StringBuilder transpositionInput = new StringBuilder(substitutionOutput.toString());
+            String transpositionInput = substitutionOutput.toString();
             int modulus = transpositionInput.length() % n;
             if (modulus != 0) {
                 modulus = n - modulus;
 
                 for (; modulus != 0; modulus--) {
-                    transpositionInput.append("/");
+                    transpositionInput += "/";
                 }
             }
             StringBuffer transpositionOutput = new StringBuffer();