Update sphinx to 2.3.1

i386-linux-deb9/Dockerfile

@@ -12,11 +12,12 @@ RUN apt-get update -qq \
     perl python3 texinfo xz-utils pxz lbzip2 bzip2 patch openssh-client sudo time \
     jq wget curl \
     # Documentation tools
-    python3-sphinx texlive-xetex texlive-latex-extra texlive-generic-extra texlive-fonts-recommended lmodern \
+    python3-pip texlive-xetex texlive-latex-extra texlive-generic-extra texlive-fonts-recommended lmodern \
     # Core build utilities
     libgmp-dev:i386 \
     && apt-get clean \
     && rm -rf /var/lib/apt/lists/*
+RUN pip3 install sphinx==2.3.1
 
 WORKDIR /tmp
 # Get i386 GHC bindist for 32 bit CI builds.

x86_64-linux-deb10/Dockerfile

@@ -25,10 +25,10 @@ RUN apt-get update -qq && apt-get install --no-install-recommends -qy \
     # For nofib
     valgrind \
     # Documentation tools
-    python3-sphinx texlive-xetex texlive-latex-extra texlive-binaries texlive-fonts-recommended lmodern texlive-generic-extra \
+    python3-pip texlive-xetex texlive-latex-extra texlive-binaries texlive-fonts-recommended lmodern texlive-generic-extra \
     && apt-get clean \
     && rm -rf /var/lib/apt/lists/*
-
+RUN pip3 install sphinx==2.3.1
 
 WORKDIR /tmp
 # Install GHC and cabal

x86_64-linux-deb9/Dockerfile

@@ -25,10 +25,11 @@ RUN apt-get update -qq && apt-get install --no-install-recommends -qy \
     # For nofib
     valgrind \
     # Documentation tools
-    python3-sphinx texlive-xetex texlive-latex-extra texlive-binaries texlive-fonts-recommended lmodern texlive-generic-extra \
+    texlive-xetex texlive-latex-extra texlive-binaries texlive-fonts-recommended lmodern texlive-generic-extra \
+    python3-pip \
     && apt-get clean \
     && rm -rf /var/lib/apt/lists/*
-
+RUN pip3 install sphinx==2.3.1
 
 WORKDIR /tmp
 # Install GHC and cabal

x86_64-linux-fedora27/Dockerfile

@@ -12,18 +12,13 @@ RUN dnf -y install coreutils binutils which git make \
     curl wget jq
 
 # Documentation tools
-RUN dnf -y install python3-sphinx \
+RUN dnf -y install python3-pip \
     texlive texlive-latex texlive-xetex \
     texlive-collection-latex texlive-collection-latexrecommended \
     texlive-xetex-def texlive-collection-xetex \
     python-sphinx-latex dejavu-sans-fonts dejavu-serif-fonts \
     dejavu-sans-mono-fonts
-
-# This is in the PATH when I ssh into the CircleCI machine but somehow
-# sphinx-build isn't found during configure unless we explicitly
-# add it here as well; perhaps PATH is being overridden by CircleCI's
-# infrastructure?
-ENV PATH /usr/libexec/python3-sphinx:$PATH
+RUN pip3 install sphinx==2.3.1
 
 # systemd isn't running so remove it from nsswitch.conf
 # Failing to do this will result in testsuite failures due to