Pass $DEBIAN_FRONTEND through make get-deps

This lets you stop `make get-deps` from demanding your timezone.

Makefile

@@ -521,7 +521,7 @@ static-docker: static scripts/*
 # We have system-level deps to install
 # We want the One True Place for them to be in the Dockerfile.
 get-deps:
-	sudo apt-get install -qq -y --no-upgrade $(shell cat Dockerfile | sed -n '/^###DEPS_BEGIN###/,$${p;/^###DEPS_END###/q}' | grep -v '^ *#' | grep -v "^RUN" | tr '\n' ' ' | tr -d '\\')
+	sudo DEBIAN_FRONTEND=$(DEBIAN_FRONTEND) apt-get install -qq -y --no-upgrade $(shell cat Dockerfile | sed -n '/^###DEPS_BEGIN###/,$${p;/^###DEPS_END###/q}' | grep -v '^ *#' | grep -v "^RUN" | tr '\n' ' ' | tr -d '\\')
 
 # And we have submodule deps to build
 deps: $(DEPS)