use pkill in start.sh to fix mac os (#845)

tests/simulation/start.sh

@@ -117,7 +117,7 @@ fi
 # Trap and ignore SIGTERM, so we don't kill this process along with its children.
 if [ "$USE_MULTITAIL" = "no" ]; then
   trap '' SIGTERM
-  trap 'kill -- -$$' SIGINT EXIT
+  trap 'pkill -P $$ beacon_node' SIGINT EXIT
 fi
 
 COMMANDS=()

vendor/nim-metrics

@@ -1 +1 @@
-Subproject commit 19c87b7dc91dfbc0b6823a3d2996869397dd34e6
+Subproject commit 71a51f34df2572df786aeb53d1c7c78bef16a7ef