deploy/build.yaml: get gendb from vuln repo

The gendb binary now lives in golang.org/x/vuln, not
the current repo (vulndb), so we have to install it
before running it.

Fixes golang/go#49449

Change-Id: I06563636d07d0a002eb3f065da0ef44bc36be24e
Reviewed-on: https://go-review.googlesource.com/c/vulndb/+/362494
Trust: Jonathan Amsterdam <jba@google.com>
Run-TryBot: Jonathan Amsterdam <jba@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Julie Qiu <julie@golang.org>
diff --git a/deploy/build.yaml b/deploy/build.yaml
index 4462af0..13af7e3 100644
--- a/deploy/build.yaml
+++ b/deploy/build.yaml
@@ -1,7 +1,8 @@
 steps:
   - name: golang
     entrypoint: bash
-    args: ["-c", "go run golang.org/x/vulndb/cmd/gendb -reports reports -out /workspace/db"]
+    args: ["-c", "go install golang.org/x/vuln/cmd/gendb@latest
+                  && gendb -reports reports -out /workspace/db"]
   - name: gcr.io/cloud-builders/gsutil
     entrypoint: bash
-    args: ["./deploy/gcp-deploy.sh"]
\ No newline at end of file
+    args: ["./deploy/gcp-deploy.sh"]