Merge branch '1.x' into 2.x

* 1.x:
  Revert "Deprecate "flex-require" sections"
  Ignore correct PHP CS Fixer config file in .gitattributes

Author: nicolas-grekas

.gitattributes

@@ -1,7 +1,7 @@
 /.github export-ignore
 /.gitattributes export-ignore
 /.gitignore export-ignore
-/.php_cs.dist export-ignore
+/.php-cs-fixer.dist.php export-ignore
 /.travis.yml export-ignore
 /phpunit.xml.dist export-ignore
 /tests export-ignore

src/Flex.php

@@ -317,9 +317,6 @@ public function update(Event $event, $operations = [])
             if (!isset($json['flex-'.$type])) {
                 continue;
             }
-
-            $this->io->writeError(sprintf('<warning>Using section "flex-%s" in composer.json is deprecated, use "%1$s" instead.</>', $type));
-
             foreach ($json['flex-'.$type] as $package => $constraint) {
                 if ($symfonyVersion && '*' === $constraint && isset($versions['splits'][$package])) {
                     // replace unbounded constraints for symfony/* packages by extra.symfony.require