[bug] cannot handle nested brace

```vim
""
" foobar
call g:foobar#utils#plugin.Flag('g:foobar',
\ get(s:foobar, 0, '')
\ )
```

It can work:

```
*foobar:g:foobar*
foobar
Default: get(s:foobar, 0, '') `
```

However, the default of nested brace cannot be detected.

```vim
""
" foobar
call g:foobar#utils#plugin.Flag('g:foobar',
\ get(split(s:foobar), 0, '')
\ )
```

```
*foobar:g:foobar*
foobar
```