Update sphinx to 2.3.1

Due to ghc#17740.

aarch64-linux-deb9/Dockerfile

@@ -19,7 +19,7 @@ RUN apt-get update \
 ENV BOOT_LLVM_DIR /opt/llvm-bootstrap
 ENV BOOT_LLVM_VERSION 7.0.0
 ENV PATH /usr/local/bin:$PATH
-RUN curl http://releases.llvm.org/$BOOT_LLVM_VERSION/clang+llvm-$BOOT_LLVM_VERSION-aarch64-linux-gnu.tar.xz | tar -xJC . && \
+RUN curl https://releases.llvm.org/$BOOT_LLVM_VERSION/clang+llvm-$BOOT_LLVM_VERSION-aarch64-linux-gnu.tar.xz | tar -xJC . && \
     mkdir $BOOT_LLVM_DIR && \
     cp -R clang+llvm*/* $BOOT_LLVM_DIR && \
     rm -R clang+llvm* && \
@@ -28,7 +28,7 @@ RUN curl http://releases.llvm.org/$BOOT_LLVM_VERSION/clang+llvm-$BOOT_LLVM_VERSI
 # GHC
 # Use 8.8.1 to bootstrap, since earlier releases are especially buggy on AArch64
 ENV GHC_VERSION 8.8.1
-RUN curl http://downloads.haskell.org/~ghc/$GHC_VERSION/ghc-$GHC_VERSION-aarch64-deb9-linux.tar.xz | tar -xJ
+RUN curl https://downloads.haskell.org/~ghc/$GHC_VERSION/ghc-$GHC_VERSION-aarch64-deb9-linux.tar.xz | tar -xJ
 WORKDIR /ghc-$GHC_VERSION
 RUN ./configure --prefix=/usr/local LLC=$BOOT_LLVM_DIR/bin/llc OPT=$BOOT_LLVM_DIR/bin/opt && \
     make install
@@ -40,7 +40,7 @@ RUN ghc --version
 ENV LLVM_DIR /opt/llvm
 ENV LLVM_VERSION 9.0.0
 ENV PATH $LLVM_DIR/bin:$PATH
-RUN curl http://releases.llvm.org/$LLVM_VERSION/clang+llvm-$LLVM_VERSION-aarch64-linux-gnu.tar.xz | tar -xJC . && \
+RUN curl https://releases.llvm.org/$LLVM_VERSION/clang+llvm-$LLVM_VERSION-aarch64-linux-gnu.tar.xz | tar -xJC . && \
     mkdir $LLVM_DIR && \
     cp -R clang+llvm*/* $LLVM_DIR && \
     rm -R clang+llvm* && \