CDRIVER-1979 use modern sphinx on evergreen

Author: ajdavis

.evergreen/config.yml

@@ -326,6 +326,18 @@ tasks:
 # Compile Matrix {{{
     - name: make-release-archive
       commands:
+        - command: shell.exec
+          type: test
+          params:
+            working_dir: "mongoc"
+            script: |
+              # Need modern Sphinx for :caption: in literal includes
+              python -m virtualenv venv
+              cd venv
+              . bin/activate
+              ./bin/pip install sphinx
+              cd ..
+
         - command: shell.exec
           type: test
           params:
@@ -336,6 +348,12 @@ tasks:
               export MONGOC_TEST_FUTURE_TIMEOUT_MS=30000
               export MONGOC_TEST_SKIP_LIVE=on
               export MONGOC_TEST_SKIP_SLOW=on
+
+              # Use modern sphinx-build from venv.
+              . venv/bin/activate
+              which sphinx-build
+              sphinx-build --version
+
               ./autogen.sh --enable-html-docs --enable-man-pages && make distcheck
         - func: "upload docs"
         - func: "upload release"