replace pkg/symlink with moby/sys/symlink

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

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

@@ -0,0 +1,17 @@
+// +build !windows
+
+package symlink
+
+import (
+	"path/filepath"
+)
+
+func evalSymlinks(path string) (string, error) {
+	return filepath.EvalSymlinks(path)
+}
+
+func isDriveOrRoot(p string) bool {
+	return p == string(filepath.Separator)
+}
+
+var isAbs = filepath.IsAbs