fix: shrinkwrap in node v10.0

See #2654 (comment)

PR-URL: #2688
Credit: @ljharb
Close: #2688
Reviewed-by: @wraithgar

lib/shrinkwrap.js

@@ -1,7 +1,7 @@
 const { resolve, basename } = require('path')
 const util = require('util')
 const fs = require('fs')
-const { unlink } = fs.promises || util.promisify(fs.unlink)
+const { unlink } = fs.promises || { unlink: util.promisify(fs.unlink) }
 const Arborist = require('@npmcli/arborist')
 const log = require('npmlog')