Cannot make an external URL the first item in the TOC

[MaxGhenis]

Describe the bug

When changing _toc.yml to make an external URL the first item:

I get this error:

Extension error:
Handler <function add_toc_to_sphinx at 0x7f1d88fa7550> for event 'config-inited' threw an exception (exception: 'file')
Traceback (most recent call last):
File "/usr/share/miniconda/envs/childallowance/lib/python3.8/site-packages/sphinx/events.py", line 110, in emit
results.append(listener.handler(self.app, *args))
File "/usr/share/miniconda/envs/childallowance/lib/python3.8/site-packages/jupyter_book/toc.py", line 192, in add_toc_to_sphinx
app.config["master_doc"] = _posix_no_suffix(toc["file"])
KeyError: 'file'

Environment

• Python Version [e.g. 3.7.1]: 3.8
• Package versions or output of jupyter-book --version: 0.8.0
• Operating System: Ubuntu

Additional context
This wasn't an issue prior to 0.8.0, as the TOC didn't display the first item:

But in 0.8.0, that external link is no longer the topmost link, as I'd like:

[choldgraf]

oops, missed this one - can you try setting

  home_page_in_navbar       : false 

That should let you exclude the home page and thus have your first link an external site

[MaxGhenis]

Thanks that worked!