create travis check for go.mod's

.travis.yml

@@ -36,6 +36,7 @@ install: true
 script:
   - make verify-kustomize
   - ./travis/kyaml-pre-commit.sh
+  - ./travis/check-go-mod.sh
 
 # TBD. Suppressing for now.
 notifications:

travis/check-go-mod.sh

@@ -0,0 +1,20 @@
+#!/bin/bash
+# Copyright 2019 The Kubernetes Authors.
+# SPDX-License-Identifier: Apache-2.0
+
+set -x
+set -e
+
+# verify all modules pass validation
+for i in $(find . -name go.mod); do
+  pushd .
+  cd $(dirname $i);
+  go list -m -json all > /dev/null
+  go mod tidy -v
+  popd
+done
+
+# verify no changes to go.mods -- these should be part of the PR
+find . -name go.sum | xargs git checkout --
+git add .
+git diff-index HEAD --exit-code