bug #797 Fixed directory separator trimming in vendors path (skmedix)

This PR was merged into the 1.13-dev branch.

Discussion
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Fixed directory separator trimming in vendors path

Fixes #796

We don't need to use `\DIRECTORY_SEPARATOR` here, as [**symfony/filesystem**](https://github.com/symfony/filesystem/blob/4.4/Filesystem.php#L451) already normalizes windows directory separator to use forward slash.

Commits
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fd34129 Fixed directory separator trimming in vendors path

Author: nicolas-grekas

src/Flex.php

@@ -520,7 +520,7 @@ function ($value) {
     private function synchronizePackageJson(string $rootDir)
     {
         $rootDir = realpath($rootDir);
-        $vendorDir = trim((new Filesystem())->makePathRelative($this->config->get('vendor-dir'), $rootDir), \DIRECTORY_SEPARATOR);
+        $vendorDir = trim((new Filesystem())->makePathRelative($this->config->get('vendor-dir'), $rootDir), '/');
 
         $synchronizer = new PackageJsonSynchronizer($rootDir, $vendorDir);