- All supported platforms can handle the same set of signals we're
  interested in, thus we don't need build contraints to use a set of
  signals on Linux, while restricting ourselves to only SIGINT on Darwin
  and Windows.
- According to the documentation of os/signal, similar to SIGINT and
  SIGTERM, SIGHUP causes the program to exit, therefore add it to the
  list of handled signals.
Signed-off-by: Rodolfo Carvalho <rcarvalh@redhat.com>