Fix CI failures (#1994)

* Try to fix build failures by updating sphinx

See sphinx-doc/sphinx#9811

* Does not work with py2, so pin old docutils

Author: Arusekk

docs/requirements.txt

@@ -1,6 +1,7 @@
 capstone
 coveralls
 doc2dash
+docutils<0.18
 isort
 mako>=1.0.0
 paramiko>=1.15.2
@@ -14,4 +15,4 @@ ropgadget>=5.3
 sphinx<3.4
 sphinx_rtd_theme
 sphinxcontrib-napoleon
-sphinxcontrib-autoprogram<=0.1.5
+sphinxcontrib-autoprogram<=0.1.5