replace pkg/symlink with moby/sys/symlink

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

vendor/github.com/moby/sys/symlink/doc.go

@@ -0,0 +1,4 @@
+// Package symlink implements EvalSymlinksInScope which is an extension of
+// filepath.EvalSymlinks, as well as a Windows long-path aware version of
+// filepath.EvalSymlinks from the Go standard library (https://golang.org/pkg/path/filepath).
+package symlink