Description

Add forward compatibility for the following change in PHPUnit 6

PHPUnit's units of code are now namespaced. For instance, PHPUnit_Framework_TestCase is now `PHPUnit\Framework\TestCase

by implementing

Added phpunit\framework\TestCase as an alias for PHPUnit_Framework_TestCase for forward compatibility

See: https://github.com/sebastianbergmann/phpunit/wiki/Release-Announcement-for-PHPUnit-6.0.0
See: https://github.com/sebastianbergmann/phpunit/blob/5.4/ChangeLog-5.4.md

How to test

Run all tests or check the logs on travis-ci.

Thanks to @GMishx for pointing out this backwards compatibility issue in #1116