Fix default in gpstime cmd to point at 'now'
This merge request addresses #14 (closed), so that when calling gpstime
with no arguments, it defaults to 'now'.
It turns out that there are some semantic differences between nargs='*'
and nargs=argparse.REMAINDER
in that the latter may not ever inherit the argument's default value when used as a positional argument. See https://bugs.python.org/issue35495.
Closes #14 (closed).