DX: cleanup .gitignore (#12)

Author: keradus

.gitignore

@@ -1,4 +1,3 @@
 /composer.lock
 /phpunit.xml
 /vendor/
-tests/GeckoPackages/DiffOutputBuilder/Tests/Integration/out

LICENSE_DIFF

@@ -3,7 +3,8 @@
 This version is for PHP CS Fixer only! Do not use it!
 
 Code from `sebastian/diff` has been forked a republished by permission of Sebastian Bergmann.
-Licenced with BSD-3-Clause @ see LICENSE_DIFF, copyright (c) Sebastian Bergmann <sebastian@phpunit.de>
+Main change is to make the package compatible with older PHP engines.
+Licenced with BSD-3-Clause @ see LICENSE, copyright (c) Sebastian Bergmann <sebastian@phpunit.de>
 https://github.com/sebastianbergmann/diff
 
 For questions visit us @ https://gitter.im/PHP-CS-Fixer/Lobby