add: initial implementation of Rabin-Karp algorithm for string matching

Author: Lohit-pro

src/main/java/com/thealgorithms/strings/PatternSearchUsingRabinKarpAlgo.java

@@ -12,7 +12,7 @@
     to confirm that it's an exact match.
 */
 
-public class PatternSearchUsingRabinKarpAlgo {
+public final class PatternSearchUsingRabinKarpAlgo {
 
     private PatternSearchUsingRabinKarpAlgo() {
     }