message: Add Gitian key for droark
  I've signed 0.18.0rc1 and 0.18.0rc2, and I intend to sign every release moving forward.
diff: @@ -6,6 +6,7 @@ C519EBCF3B926298946783EFF6430754120EC2F4 Christian Decker (cdecker)
  F20F56EF6A067F70E8A5C99FFF95FAA971697405 centaur
  C060A6635913D98A3587D7DB1C2491FFEB0EF770 Cory Fields
  BF6273FAEF7CC0BA1F562E50989F6B3048A116B5 Dev Random
  +6D3170C1DC2C6FD0AEEBCA6743811D1A26623924 Douglas Roark
  9A1689B60D1B3CCE9262307A2F40A9BF167FBA47 Erik Mossberg (erkmos)
  D35176BE9264832E4ACA8986BF0792FBE95DC863 fivepiece
  01CDF4627A3B88AAE4A571C87588242FBE38D3A8 Gavin Andresen
  