Empty files are missing

Hi,

I'm using `wskdeploy` to deploy a nodejs project. Some of my dependencies under `node_modules` contains empty files, that are currently ignored by `wskdeploy`:
https://github.com/apache/openwhisk-wskdeploy/blob/d653592d8b8e8b7e64f228049bfa2f74db07a1e1/utils/zip.go#L79-L81

Unfortunately, the missing files currently break my application.

Is the empty check really needed?
How can I ensure that empty files will be uploaded?

My workaround:
```bash
find . -type f -empty -name '*.js' -exec bash -c "echo '//' > \"{}\"" \;
```

Start in utils/zip.go at the linked lines 79-81 and inspect why zero-byte files are excluded during deployment packaging. Reproduce with an empty JavaScript file in a node_modules dependency, then verify that the file is included in the uploaded archive without requiring the workaround shown in the issue.

Written by the indexing model from the issue text.