Add linting to Kokoro + deprecate CircleCI

.kokoro/lint.cfg

@@ -0,0 +1,7 @@
+# Format: //devtools/kokoro/config/proto/build.proto
+
+# Tell the trampoline which build file to use.
+env_vars: {
+    key: "TRAMPOLINE_BUILD_FILE"
+    value: "github/nodejs-docs-samples/.kokoro/lint.sh"
+}

.kokoro/lint.sh

@@ -0,0 +1,28 @@
+#!/bin/bash
+
+# Copyright 2018 Google LLC.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+export GCLOUD_PROJECT=nodejs-docs-samples-tests
+export NODE_ENV=development
+
+cd github/nodejs-docs-samples/
+
+# Install dependencies
+npm install
+
+# Run lint
+npm run lint
+
+exit $?