Base64 may not be URL safe

[Rohitrajak1807]

https://github.com/hnasr/javascript_playground/blob/bc01f3c07fef893ceefd465fb32b655b36b1b214/sharding/index.js#L65

@hnasr base64 encoding used in the URL shortener may have a '/' un the URL_ID, so using digest('base64url') is advised to avoid this.