Codeigniter 3.1.6 with PHP7.1 and Nginx

Thanks for the continuous updates. Last week I have installed php7.1 on my development machine in order to upgrade all the company's websites. Every think is seems fixed now except the following errors.

A PHP Error was encountered
Severity: 8192
Message: Function mcrypt_get_iv_size() is deprecated
Filename: libraries/Encrypt.php
Line Number: 315

A PHP Error was encountered

Severity: 8192

Message: Function mcrypt_decrypt() is deprecated

Filename: libraries/Encrypt.php
Line Number: 325

I am using codeigniter 3.1.6 though.
It seems like required to update the core Encrypt.php where the functions are mcrypt_get_iv_size() and mcrypt_decrypt() as they are deprecated.

Could you help me how to fix the core lib error or should I wait for next release as I use this Encrypt lib many places?
Your help in this regards will be helpful.

  codeigniter error.jpg (Size: 215.48 KB / Downloads: 5)