Fix unstaged deleted diff

2cbd38e2edca6ae6aa732b7afb809fb4b2a7dbf0 broke displaying the diff for an unstaged deleted file.  In the call to `cmds.do(cmds.Diff, ...)`, `item.deleted` was being passed as a positional argument, which meant it was actually being assigned to the `cached` argument, rather than the `deleted` argument, resulting in an empty diff.  Change to pass as a keyword argument to avoid this.