Multiple sources

Hi,

I have a problem with multi source files. My configuration:
```
babel: {
options: {
minified: true
},
plugins: {
files: {
'dir/min/plugins.min.js': [
'dir/plugins.core.file.js',
'dir/plugins/*.js' // single plugin files -- IGNORED!!! Why?
]
}
}
},
```
but output (destination) file is created based only on `dir/plugins.core.file.js` and rest of sources (`dir/plugins/*.js`) are ignored.

What am I doing wrong?

Start by reproducing the configuration with dir/plugins.core.file.js and the dir/plugins/*.js glob, then trace how the plugins.files source array is processed. Done means the generated dir/min/plugins.min.js includes both the explicitly listed file and the files matched by the glob.

Written by the indexing model from the issue text.