package/proftpd: fix group name preventing server from starting

Replace the group name 'nogroup' with 'nobody' in the default ProFTPD
configuration file. This fixes the following error when starting the
server:

  proftpd[110]: fatal: Group: Unknown group 'nogroup' on line 30 of '/etc/proftpd.conf'

Fixes: 0d887cc2b4 ("system: replace nogroup with nobody")
Signed-off-by: Mattia Narducci <mattianarducci1@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/proftpd/proftpd.mk

@@ -130,6 +130,7 @@ endif
 define PROFTPD_INSTALL_TARGET_CMDS
 	$(INSTALL) -D -m 0755 $(@D)/proftpd $(TARGET_DIR)/usr/sbin/proftpd
 	$(INSTALL) -m 0644 -D $(@D)/sample-configurations/basic.conf $(TARGET_DIR)/etc/proftpd.conf
+	$(SED) 's/^\(Group\s\+\)nogroup/\1nobody/' $(TARGET_DIR)/etc/proftpd.conf
 	$(PROFTPD_INSTALL_FTPQUOTA)
 	$(PROFTPD_INSTALL_FTPASSWD)
 endef