minor #8483 added /var/sessions folder (OskarStark)

This PR was merged into the 3.3 branch.

Discussion
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added /var/sessions folder

Based on this change: symfony/symfony-standard@dcf4ead, introduced in 3.3.9

Commits
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82a1866 added /var/sessions folder

Author: xabbuh

deployment/platformsh.rst

@@ -64,6 +64,7 @@ Platform.sh how to deploy your application (read more about
     mounts:
         '/var/cache': 'shared:files/cache'
         '/var/logs': 'shared:files/logs'
+        '/var/sessions': 'shared:files/sessions'
 
     # The hooks that will be performed when the package is deployed.
     hooks: