Handle camel case keys in json `.env` files.

Hi Strongloop,

I _needed_ foreman to handle camel case keys in json `.env` files:
```
{
  "someAwesomeService": {
     "appId": "foobar",    # => SOME_AWESOME_SERVICE_APP_ID="foobar"
     "apiKey": "secret"   # => SOME_AWESOME_SERVICE_API_KEY="secret"
  }
}
```

This PR delivers this feature and associated tests.

Note: While I was able to make the updated tests pass, I was unable to run some unrelated tests (neither before and after update.). Is there any special env to be set up?
I appreciate the effort to keep the style consistent. Since the input/output are simple strings, I think in this case I would just do:
```js
// Given: "camelCaseString"
// Get: "CAMEL_CASE_STRING"
```