Make utility classes constructors private

Author: vsbogd

src/main/java/io/singularitynet/sdk/common/Utils.java

@@ -9,6 +9,9 @@
 
 public class Utils {
 
+    private Utils() {
+    }
+
     public static byte[] strToBytes(String str) {
         return str.getBytes(UTF_8);
     }

src/main/java/io/singularitynet/sdk/ethereum/CryptoUtils.java

@@ -11,6 +11,9 @@
 
 public class CryptoUtils {
 
+    private CryptoUtils() {
+    }
+
     public static Address getSignerAddress(byte[] message, byte[] signature) {
         return Utils.wrapExceptions(() -> {
             Sign.SignatureData signatureData = bytesToSignature(signature);