Do not hardcode default hb alert timeout (#222)

Author: satterly

alertaclient/commands/cmd_heartbeats.py

@@ -10,7 +10,7 @@
 @click.command('heartbeats', short_help='List heartbeats')
 @click.option('--alert', is_flag=True, help='Alert on stale or slow heartbeats')
 @click.option('--severity', '-s', metavar='SEVERITY', default='major', help='Severity for stale heartbeat alerts')
-@click.option('--timeout', metavar='SECONDS', default=86000, type=int, help='Seconds before stale heartbeat alerts will be expired')
+@click.option('--timeout', metavar='SECONDS', type=int, help='Seconds before stale heartbeat alerts will be expired')
 @click.option('--purge', is_flag=True, help='Delete all stale heartbeats')
 @click.pass_obj
 def cli(obj, alert, severity, timeout, purge):