MAGETWO-48291: [Github] Permissions Error When Running `bin/magento setup:upgrade`

- skipping writable checks for symlinked files/folders

setup/src/Magento/Setup/Model/FilePermissions.php

@@ -151,7 +151,7 @@ class FilePermissions
 
         try {
             foreach ($directoryIterator as $subDirectory) {
-                if (!$subDirectory->isWritable()) {
+                if (!$subDirectory->isWritable() && !$subDirectory->isLink()) {
                     $this->nonWritablePathsInDirectories[$directory][] = $subDirectory;
                     $foundNonWritable = true;
                 }