docs: Update spawn.txt
docs: Update spawn.txt

Add the : to the process name in the pkill command otherwise pkill may
match vim when editing receiptomatic-www.c

Signed-off-by: Andrew Clayton <02e0a999c50b1f88df7a8f5a04e1b76b35ea6a88@opentechlabs.co.uk>

ac000/receiptomatic