stubby: standardize on ca-bundle cert dependency

Using ca-bundle package saves 10KB over using ca-certificates, and with
commit openwrt/openwrt@191078e83d is a drop-in
replacement for packages using openssl and CA certs. This has been noted
as the default in current trunk by other packages switching over e.g.
openwrt@e0a5ed9f76.

For further related discussion see:
openwrt#7030 (comment) and
openwrt#6682 (comment).

Signed-off-by: Tony Ambardar <itugrok@yahoo.com>

net/stubby/Makefile

@@ -36,7 +36,7 @@ define Package/stubby
 	SUBMENU:=IP Addresses and Names
 	TITLE+= - (daemon that uses getdns)
 	USERID:=stubby=410:stubby=410
-	DEPENDS:= +libyaml +getdns +ca-certificates
+	DEPENDS:= +libyaml +getdns +ca-bundle
 endef
 
 define Package/stubby/description