Fix copybutton.js

[skrah]

For some reason copybutton.js does not always work in the combined docs, e.g. here:

https://xnd.readthedocs.io/en/latest/xnd/types.html

@xmnlab Do you have any ideas what the cause is?

[xmnlab]

@skrah

I can take a look. do you know some page that it is working?

[skrah]

It worked in my home build with your latest patch, and it used to work on e.g. ndtypes.readthedocs.io, but it no longer does.

So it's probably entirely unrelated to the combined docs and your patch.

[skrah]

Here's a page that works, but of course not on readthedocs:

https://docs.scipy.org/doc/scipy/reference/tutorial/fftpack.html

[xmnlab]

I see .. the ">>>" button, right? I will take a look into that now 👍

[xmnlab]

I saw there is an opened issue about that on readthedocs: readthedocs/sphinx_rtd_theme#429