def set(key, value, expires: nil)
      validate_key(key)
      validate_value(value)

      mset({ key => value }, expires: expires)
    end
def set(key, value, expires: nil)
      validate_key(key)
      validate_value(value)

      mset({ key => value }, expires: expires)
    end
set :: String, String, expires: Time? -> nil

 Sets the specified key to the specified value. Returns nil. Raises on
 error.

 Example:

   kv.set("foo", "bar")
     # => nil