Prevent zipping dot files

When I have the following target for compress:

```
    gnap: {
        options: {
            archive: './releases/GNaP.Themes.Web.GNaP/gnap.zip',
            mode: 'zip'
        },
        files: [{ expand: true, cwd: './deploy/', src: ['**'] }]
    }
```

I end up with a zip file called gnap.zip, as intended. However, when looking inside the zip, at the root we see a file called "." being part of the zip. I suspect this is due the expand from the files, expanding everything, including "." as the base.

I added an if statement to exclude "." files from the archive. Another solution might be to have some sort of exclude list option?