functions/slack: config.json -> env vars (GoogleCloudPlatform#1751)

**Do not merge** until @labtopia updates the docs accordingly.

Author: Ace Nassri

functions/slack/index.js

@@ -15,7 +15,6 @@
 'use strict';
 
 // [START functions_slack_setup]
-const config = require('./config.json');
 const {google} = require('googleapis');
 const {verifyRequestSignature} = require('@slack/events-api');
 
@@ -94,7 +93,7 @@ const formatSlackMessage = (query, response) => {
  */
 const verifyWebhook = (req) => {
  const signature = {
- signingSecret: config.SLACK_SECRET,
+ signingSecret: process.env.SLACK_SECRET,
  requestSignature: req.headers['x-slack-signature'],
  requestTimestamp: req.headers['x-slack-request-timestamp'],
  body: req.rawBody,
@@ -118,7 +117,7 @@ const makeSearchRequest = (query) => {
  return new Promise((resolve, reject) => {
  kgsearch.entities.search(
  {
- auth: config.KG_API_KEY,
+ auth: process.env.KG_API_KEY,
  query: query,
  limit: 1,
  },

functions/slack/test/index.test.js

@@ -43,7 +43,7 @@ const getSample = () => {
  return {
  program: proxyquire('../', {
  googleapis: {google: googleapis},
- './config.json': config,
+ process: { env: config },
  '@slack/events-api': eventsApi,
  }),
  mocks: {