message: Update date in comment about default SSL ciphers
diff: #ifdef HAVE_LIBSSL
  // Copypasted from
  // https://wiki.mozilla.org/Security/Server_Side_TLS#Intermediate_compatibility_.28default.29
  -// at 2016-06-03
  +// at 2018-04-01
  static CString ZNC_DefaultCipher() {
  return "ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305:ECDHE-"
  "ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-"
  