test: enable cyrillic punycode test case

The test from RFC 3492 contains a bug: the uppercase D in the input
should be lowercased.  Fix that and enable the test.

Fixes: https://github.com/nodejs/node/issues/8691
PR-URL: https://github.com/nodejs/node/pull/8695
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>
Reviewed-By: Ilkka Myller <ilkka.myller@nodefield.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

test/parallel/test-punycode.js

@@ -62,12 +62,10 @@ var tests = {
       '\uC744\uAE4C',
 
   // (I) Russian (Cyrillic)
-  /* XXX disabled, fails - possibly a bug in the RFC
-  'b1abfaaepdrnnbgefbaDotcwatmq2g4l':
+  'b1abfaaepdrnnbgefbadotcwatmq2g4l':
       '\u043F\u043E\u0447\u0435\u043C\u0443\u0436\u0435\u043E\u043D\u0438' +
       '\u043D\u0435\u0433\u043E\u0432\u043E\u0440\u044F\u0442\u043F\u043E' +
       '\u0440\u0443\u0441\u0441\u043A\u0438',
-  */
 
   // (J) Spanish: Porqu<eacute>nopuedensimplementehablarenEspa<ntilde>ol
   'PorqunopuedensimplementehablarenEspaol-fmd56a':