Convert the otp value to ascii from unicode

Othersise the clipboard library fails in my system
because it's not expecting unicode.

softtoken/softtoken.py

@@ -156,7 +156,7 @@ def main():
         k = PyKeyboard()
         k.type_string(otp)
     elif args.copy_clipboard:
-        pyperclip.copy(otp)
+        pyperclip.copy(otp.encode('ascii'))
     else:
         print(otp)