docutils>=0.19 broke the tests, which upstream fixed in a newer
commit. Cherry-pick it.
* gnu/packages/patches/python-sphinx-prompt-docutils-0.19.patch: New file.
* gnu/local.mk (dist_patch_DATA): Register it.
* gnu/packages/sphinx.scm (python-sphinx-prompt)[origin]: Use it.
Change-Id: I597387a35e6a1da01063b4812e0f919788a13b54
