replace IllegalArgumentException with require

src/commonMain/kotlin/com/infendro/otp/HOTP.kt

@@ -25,8 +25,7 @@ class HOTP(
         secret: UByteArray,
         counter: Long,
     ): String {
-        if (counter < 0)
-            throw IllegalArgumentException()
+        require(counter >= 0)
 
         val hash = generateHash(secret, counter.toUByteArray())
         return otp(hash)