Gitter webhook mandatory

[raisedadead]

Describe the bug

Seems like Gitter Webhook is mandatory in config

To Reproduce

~/DEV/open-api staging 7s
❯ yarn start
yarn run v1.6.0
$ cross-env DEBUG=fcc:* nodemon node_modules/serverless/bin/serverless offline start --skipCacheInvalidation
[nodemon] 1.17.3
[nodemon] to restart at any time, enter `rs`
[nodemon] watching: *.*
[nodemon] starting `node node_modules/serverless/bin/serverless offline start --skipCacheInvalidation`

 Serverless Warning --------------------------------------

  A valid environment variable to satisfy the declaration 'env:GITTER_WEBHOOK' could not be found.

  Serverless Error ---------------------------------------

  Invalid variable syntax when referencing file "./src/config/secrets.js". Check if your javascript is returning the correct data.

  Get Support --------------------------------------------
     Docs:          docs.serverless.com
     Bugs:          github.com/serverless/serverless/issues
     Forums:        forum.serverless.com
     Chat:          gitter.im/serverless/serverless

  Your Environment Information -----------------------------
     OS:                     darwin
     Node Version:           8.11.1
     Serverless Version:     1.26.1

[nodemon] app crashed - waiting for file changes before starting...

Expected behavior

Should it be mandatory 🤷‍♂️

[ojongerius]

I noticed that, and it's ugly.

We only use it for deployments, shall we add an empty string for it in sample.env?