Document argument parsing change in test

There were explicit changes in argument parsing behavior since 10.1.1, but there also seems to be some undocumented changes in handling of some parameters. I actually think the new behavior is more sane, so here's a pr to document the current behavior in tests.

In 10.1.1, 'empty' args were not included in the arg array returned from `parse_task_string`. In 10.3.2 'empty' args are pass as empty string.


```
# 10.3.2
name, args = @app.parse_task_string("name[one,]") 

name # => 'name'
args # => ['one', '']
```

```
# 10.1.1
name, args = @app.parse_task_string("name[one,]") 

name # => 'name'
args # => ['one']
```