[Performance] avoid an unnecessary slice

Author: ljharb

lib/async.js

@@ -216,7 +216,7 @@ module.exports = function resolve(x, options, callback) {
                     var rel = rfile.slice(0, rfile.length - exts[0].length);
                     var r = opts.pathFilter(pkg, x, rel);
                     if (r) return load(
-                        [''].concat(extensions.slice()),
+                        [''].concat(extensions),
                         path.resolve(dir, r),
                         pkg
                     );