Makefile: set project ID for docker runs.

Without this, the server fails on startup due to the project being
empty.

Change-Id: I9f06d8d6241264dbb2b7b5eab332c0d09a3505bf
Reviewed-on: https://go-review.googlesource.com/c/pkgsite-metrics/+/708376
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Ethan Lee <ethanalee@google.com>

Makefile

diff --git a/Makefile b/Makefile
index 8b87c12..b808169 100644
--- a/Makefile
+++ b/Makefile
@@ -55,6 +55,7 @@
 
 DOCKER_RUN_ARGS := --rm --privileged -p 8080:8080 \
 	--env GO_ECOSYSTEM_BINARY_BUCKET=go-ecosystem \
+	--env GOOGLE_CLOUD_PROJECT=go-ecosystem \
 	$(DOCKER_AUTH_ARGS)
 
 DOCKER_ID_FILE := /tmp/ecosystem-docker-container-id