minor #2670 AbstractFixer: use applyFix instead of fix (Slamdunk)
minor #2670 AbstractFixer: use applyFix instead of fix (Slamdunk)

This PR was submitted for the master branch but it was merged into the 2.2 branch instead (closes #2670).

Discussion
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AbstractFixer: use applyFix instead of fix

Stated that:
1. `AbstractFixer` is `@internal`
1. `applyFix` is mandatory
1. Tests pass
1. https://github.com/FriendsOfPHP/PHP-CS-Fixer/blob/v2.2.0/doc/COOKBOOK-FIXERS.md#step-1---creating-files

`fix` should be final

Commits
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bc18db4 AbstractFixer: use applyFix instead of fix

FriendsOfPHP/PHP-CS-Fixer,kubawerlos/PHP-CS-Fixer,lucasmichot/PHP-CS-Fixer,kubawerlos/PHP-CS-Fixer,GrahamCampbell/PHP-CS-Fixer,SpacePossum/PHP-CS-Fixer,keradus/PHP-CS-Fixer,gharlan/PHP-CS-Fixer,Slamdunk/PHP-CS-Fixer,lucasmichot/PHP-CS-Fixer,SpacePossum/PHP-CS-Fixer,FriendsOfPHP/PHP-CS-Fixer,gharlan/PHP-CS-Fixer,Soullivaneuh/PHP-CS-Fixer,GrahamCampbell/PHP-CS-Fixer,keradus/PHP-CS-Fixer,Soullivaneuh/PHP-CS-Fixer,Slamdunk/PHP-CS-Fixer