title: Firebase deploy error - Cannot find module 'firebase'
body: <p>I'm trying to deploy Google Cloud function triggers that trigger from db events, but when I run <code>firebase deploy</code> The functions aren't deployed properly and I get an error saying <code>Error: Cannot find module firebase</code></p>
  
  <p>When I was first creating the project I could deploy functions without any issues. It's been a few days since I last deployed anything, but now I'm getting this issue on all my functions (not just my trigger functions)</p>
  
  <p>My function:</p>
  
  <pre><code>exports.deleteNotificationOnUnlike = functions
      .region("us-central1")
      .firestore.document("likes/{id}")
      .onDelete((snapshot) =&gt; {
          return db
              .doc(`/notifications/${snapshot.id}`)
              .delete()
              .catch((err) =&gt; console.error(err));
      });
  </code></pre>
  
  <p>Package.json</p>
  
  <pre><code>{
    "name": "functions",
    "description": "Cloud Functions for Firebase",
    "scripts": {
      "serve": "firebase serve --only functions",
      "shell": "firebase functions:shell",
      "start": "npm run shell",
      "deploy": "firebase deploy --only functions",
      "logs": "firebase functions:log"
    },
    "engines": {
      "node": "8"
    },
    "dependencies": {
      "busboy": "^0.3.1",
      "firebase-admin": "^8.0.0",
      "firebase-functions": "^3.1.0"
    },
    "devDependencies": {
      "firebase-functions-test": "^0.1.6"
    },
    "private": true
  }
  
  </code></pre>
  
  <p>Expecting the functions to deploy successfully but getting this error:</p>
  
  <p>Error messages from firebase:</p>
  
  <pre><code>Code in file index.js can't be loaded.
  Did you list all required modules in the package.json dependencies?
  Detailed stack trace: Error: Cannot find module 'firebase'
      at Function.Module._resolveFilename (module.js:548:15)
      at Function.Module._load (module.js:475:25)
      at Module.require (module.js:597:17)
      at require (internal/module.js:11:18)
      at Object.&lt;anonymous&gt; (/srv/handlers/users.js:5:18)
      at Module._compile (module.js:653:30)
      at Object.Module._extensions..js (module.js:664:10)
      at Module.load (module.js:566:32)
      at tryModuleLoad (module.js:506:12)
      at Function.Module._load (module.js:498:3)
  </code></pre>
  
  <pre><code>{"@type":"type.googleapis.com/google.cloud.audit.AuditLog","status":{"code":3,"message":"INVALID_ARGUMENT"},"authenticationInfo":{"principalEmail":"*********"},"requestMetadata":{"requestAttributes":{},"destinationAttributes":{}},"serviceName":"cloudfunctions.googleapis.com","methodName":"google.cloud.functions.v1.CloudFunctionsService.CreateFunction","resourceName":"projects/*******/locations/us-central1/functions/createNotificationOnComment"}
  </code></pre>
  
  <p>I've seen some posts where people were missing some modules and needed to run an <code>npm i XXX</code> inside the functions folder, but I haven't seen any instances where it was saying that the firebase module couldn't be found, and I'm not sure what changes from my last successful deployment, or what module I might be missing.</p>