Bump eslint-plugin-promise from 4.2.1 to 5.1.0 in /functions

Bumps [eslint-plugin-promise](https://github.com/xjamundx/eslint-plugin-promise) from 4.2.1 to 5.1.0.
- [Release notes](https://github.com/xjamundx/eslint-plugin-promise/releases)
- [Changelog](https://github.com/xjamundx/eslint-plugin-promise/blob/development/CHANGELOG.md)
- [Commits](https://github.com/xjamundx/eslint-plugin-promise/commits)

---
updated-dependencies:
- dependency-name: eslint-plugin-promise
  dependency-type: direct:development
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

functions/package.json

@@ -14,14 +14,13 @@
     "firebase-functions": "^3.13.1",
     "node-fetch": "^2.6.1",
     "simple-oauth2": "^3.4.0",
-    "stripe": "^8.71.0",
     "twilio": "^3.63.0",
     "uuidv4": "^6.2.6",
     "yup": "^0.32.9"
   },
   "devDependencies": {
     "eslint": "^7.19.0",
-    "eslint-plugin-promise": "^4.0.1",
+    "eslint-plugin-promise": "^5.1.0",
     "firebase-functions-test": "^0.2.3",
     "firebase-tools": "^9.2.2",
     "prettier": "^2.2.1"