Update file expand behavior

`getRelativeFileList` was stepping through patterns rather than passing them all to `grunt.file.expand` leading to exclusions (`!`) being skipped since they remove rather than add files to the list.

Example usage that led to the behavior:
```js
jasmine: {
  options: {
    specs: ['specs/**/*.js', '!specs/exclude.js']
  }
}

// Before: includes everything in specs, including specs/exclude.js
// After: excludes specs/exclude.js
```