Error: Error parsing triggers: Cannot find module 'firebase-functions'.?

How can I solve this below error?

Error: Error parsing triggers: Cannot find module 'firebase-functions'
Require stack:
- D:\budgram\functions\index.js
- C:\Users\91998\AppData\Roaming\npm\node_modules\firebase-tools\lib\triggerParser.js

Try running "npm install" in your functions directory before deploying.

package.json file here...

package.json

{
  "name": "functions",
  "description": "Cloud Functions for Firebase",
  "scripts": {
    "serve": "firebase emulators:start --only functions",
    "shell": "firebase functions:shell",
    "start": "npm run shell",
    "deploy": "firebase deploy --only functions",
    "logs": "firebase functions:log"
  },
  "engines": {
    "node": "8"
  },
  "main": "index.js",
  "dependencies": {
    "firebase-admin": "^8.10.0",
    "firebase-functions": "^3.6.1",
    "request-promise": "^4.2.6"
  },
  "devDependencies": {
    "firebase-functions-test": "^0.2.0"
  },
  "private": true
}