Composer Conflict

Hey I learn about sublime mastery, but I stuck because of composer, anyone can help me? I tried it to install fabpot but fabpot is obsolete, so I install the recommendation composer require friendsofphp/php-cs-fixer, but it say that conflict occur in my composer Problem 1

• Installation request for friendsofphp/php-cs-fixer ^2.6 -> satisfiable by friendsofphp/php-cs-fixer[v2.6.0].
• friendsofphp/php-cs-fixer v2.6.0 requires sebastian/diff ^1.4 -> satisfiable by sebastian/diff[1.4.0, 1.4.1, 1.4.2, 1.4.3, 1.4.x-dev] but these conflict with your requirements or minimum-stability.

Installation failed, reverting ./composer.json to its original content. How to fix this? Thank you