fix(cloud-function): add foreman dependency necessary for running npm start

[LeoMcA]

Before

npm start  

> mdn-function@0.0.1 start
> nf start

sh: line 1: nf: command not found

After

npm start

> mdn-function@0.0.1 start
> nf start

(node:254566) [DEP0060] DeprecationWarning: The `util._extend` API is deprecated. Please use Object.assign() instead.
(Use `node --trace-deprecation ...` to show where the warning was created)
5:36:09 PM server.1 |  > mdn-function@0.0.1 server:watch
5:36:09 PM server.1 |  > nodemon --exec npm run server
...