Fix rake task with option
Fix rake task with option

If we use rake tasks with option (`bundle exec rake db:create --trace`),
`--trace` option captured by Test::Unit automatic runner.

```
invalid option: --trace
Test::Unit automatic runner.
Usage: /home/mtsmfm/.rbenv/versions/2.3.0/bin/rake [options] [-- untouched arguments]
    -r, --runner=RUNNER              Use the given RUNNER.
...
```

test-unit/test-unit-rails,test-unit/test-unit-rails