add scrypt pbkdf

test/spec/pbkdf.js

@@ -0,0 +1,16 @@
+'use strict';
+
+const crypto = require ('../../index');
+
+describe ('hashing', () => {
+  it ('scrypt', async () => {
+    const hash = await crypto.pbkdf_scrypt ('a', 'b');
+    expect (
+      hash
+    )
+      .toEqual (
+      // eslint-disable-next-line max-len
+        '1c357645d521cce3d015441a4215814d8acbf98ed671880ba369039784de05043f0fd9867a0f265b6e5303da202ec4d541bd11752079d8f490ed1fc52e547497'
+      );
+  });
+});