Update 20-start.sh

Signed-off-by: Tyler Spires <shadrach145@gmail.com>

s6/debian-root/etc/cont-init.d/20-start.sh

@@ -14,7 +14,9 @@ $bashCmd /start.sh
 if [ -n "$PYTEST" ]; then 
     sed -i 's/^gravity_spinup$/#gravity_spinup # DISABLED FOR PYTEST/g' "$(which gravity.sh)" 
 fi
-gravity.sh
+if [ ! -n "$SKIPGRAVITYONBOOT" ]; then
+    gravity.sh
+fi
 
 # Kill dnsmasq because s6 won't like it if it's running when s6 services start
 kill -9 $(pgrep pihole-FTL) || true