Add dnsmasq to bootstrap

- Required by aiy-board-gadget

Change-Id: I5e61ed624ec51dac987488188f64d3dc90322220
diff --git a/preamble.mk b/preamble.mk
index fe65a39..a954c52 100644
--- a/preamble.mk
+++ b/preamble.mk
@@ -29,6 +29,7 @@
 	debian-faq \
 	dialog \
 	dmidecode \
+	dnsmasq \
 	doc-debian \
 	ethtool \
 	file \