message: Fix strMessageMagic
diff: @@ -17,4 +17,4 @@ std::string FormatStateMessage(const CValidationState &state)
  state.GetRejectCode());
  }
  -const std::string strMessageMagic = "Bitcoin Signed Message:\n";
  +const std::string strMessageMagic = "Qtum Signed Message:\n";
  