The "exclude" list in .analysis_options is ignored by the dartanalyzer cli

When I define excludes in my `.analysis_options` file like this:

``` yaml
analyzer:
  strong-mode: true
  exclude:
    - test/**
    - lib/generated_library/**
```

files in `lib/generated_library` are still analyzed, when they are imported by other libraries in my project.

I would expect _not_ to get strong-mode warnings or lint errors in any files excluded in the `exclude:` list
