bpo-42843: Keep Sphinx 1.8 and Sphinx 2 compatibility (GH-24282)

diff --git a/Doc/conf.py b/Doc/conf.py
index 6b88c23..cf25098 100644
--- a/Doc/conf.py
+++ b/Doc/conf.py
@@ -237,3 +237,5 @@
 # bpo-40204: Disable warnings on Sphinx 2 syntax of the C domain since the
 # documentation is built with -W (warnings treated as errors).
 c_warn_on_allowed_pre_v3 = False
+
+strip_signature_backslash = True