message: update to latest slack api client
diff: {
  "name": "botbuilder-adapter-slack",
  - "version": "1.0.4",
  + "version": "1.0.5",
  "description": "Connect Botkit or BotBuilder to Slack",
  "main": "./lib/index.js",
  "typings": "./lib/index.d.ts",
  "url": "https://github.com/howdyai/botkit.git"
  },
  "dependencies": {
  - "@slack/client": "^4.7.0",
  + "@slack/web-api": "^5.2.0",
  "botbuilder": "^4.5.2",
  "botkit": "^4.5.0",
  "debug": "^4.1.0"
  