build: run npm audit as part of ci test

Change-Id: I36c2b309464d22e2b8c27c956f21b62d4f484655
Reviewed-on: https://go-review.googlesource.com/c/vscode-go/+/397114
Trust: Hyang-Ah Hana Kim <hyangah@gmail.com>
Run-TryBot: Hyang-Ah Hana Kim <hyangah@gmail.com>
TryBot-Result: kokoro <noreply+kokoro@google.com>
Reviewed-by: Robert Findley <rfindley@google.com>

build/all.bash

@@ -49,6 +49,7 @@ run_test() {
   npm run unit-test
   npm test --silent
   npm run lint
+  npm audit
 
   echo "**** Run settings generator ****"
   go run tools/generate.go -w=false -gopls=true