helpers.makeParam should return a flat array after expanding

If the `param` is an array, the `makeParam()` function now simply appends the result of `grunt.file.expand()` to the `paramValue` array which results in nested arrays.

This later causes problems in closure builder command with `inputs` parameter. Multiple inputs should be entered like this:

```
-i path1 -i path2 -i path3
```

but now are entered like this (single, comma separated list):

```
-i path1,path2,path3
```

Therefore I think that the result of `grunt.file.expand()` should be concatenated with `paramValue` to create a flat array.