As an admin I can run passbolt using php 7.1



Q1. What is the problem that you are trying to solve?
Currently 7.1 is not officially supported by passbolt.
The mcrypt extension is deprecated on PHP 7.1

Q2 - Who is impacted?

Q3 - Why is it important and/or urgent?
Security, reducing technological debt.

Q4 - What is your proposed solution? (optional)
Migrate to cakephp3 and fix travis 7.1 build.


Now supported with v2.0.0-RC1!