Update sphinx_rtd_theme to 68a19ca / 0.4.3.dev0.

[Chris Johns]

On 2/3/20 8:53 am, Chris Johns wrote:
> On 26/2/20 3:28 pm, Amar Takhar wrote:
>> On 2020-02-26 15:27 +1100, Chris Johns wrote:
>>>
>>> Great, I am OK with the patch being pused. If it breaks on sync it will show in
>>> the build not updating and I am sure we can sort it out.
>>
>> Okay great I'll do that now then thank you!
>>
> 
> The online docs failed to build. The error is:
> 
> Theme error:
> unsupported theme option 'genindex' given
> 
> Has the minimum required version of Sphinx changed from 1.3 to something else?

I have updated my sync.rtems.org builder virtualevn's Sphinx to 1.8 using pip
however sphinxcontrib-bibtex is stuck on 0.3.5 and our configure check fails ...

https://git.rtems.org/rtems-docs/tree/common/waf.py#n229

Running `pip install --upgrade sphinxcontrib-bibtex` fails with an error, it
seems to want Sphinx >= 2.0. The sync.rtems.org virtualenv command is python 2.7
and `pip install sphinx` only installs 1.8.5. I am wondering if this is a python
2 and 3 issue and later sphinx versions need python3. I cannot find a virtualenv
for 3.6 on sync.rtems.org and forcing the 2.7 virtualenv to use 3.6 crashes.

Chris