add vet command to all.bash

Support "all.bash vet". All the other linters have their own commands.

I use this in a pre-push hook for basic validation before sending a CL.

Change-Id: I5fbc4db3767f5dab80c9224a9ebc07ef5aac6e35
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/781860
kokoro-CI: kokoro <noreply+kokoro@google.com>
LUCI-TryBot-Result: golang-scoped@luci-project-accounts.iam.gserviceaccount.com <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Ethan Lee <ethanalee@google.com>
Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>

all.bash

diff --git a/all.bash b/all.bash
index 1f383ad..cad374c 100755
--- a/all.bash
+++ b/all.bash
@@ -257,6 +257,8 @@
   unparam        - (lint) run unparam on source files
   prettier       - (lint, nonstandard) run prettier on .js and .css files.
   templates      - (lint, nonstandard) run go-template-lint on templates
+  vet            - (lint) run vet on source files
+
 EOUSAGE
 }
 
@@ -358,6 +360,7 @@
       ;;
     templates) check_templates ;;
     unparam) check_unparam ;;
+    vet) check_vet ;;
     script_hashes) check_script_hashes ;;
     build_static) run_build_static ;;
     npm) run_npm ${@:2} ;;