Update CI scripts with new Sphinx versions

.github/workflows/unit_tests.yml

@@ -8,8 +8,9 @@ jobs:
       matrix:
         python-version: [3.5, 3.6, 3.7, 3.8]
         sphinx-version:
-          - 3.0.0
-          - git+https://github.com/sphinx-doc/[email protected]
+          - 3.0.4
+          - 3.1.1
+          - git+https://github.com/sphinx-doc/[email protected]
           - git+https://github.com/sphinx-doc/[email protected]
           # master (Sphinx 4) will require at least Python 3.6, so disable it for now
           #- git+https://github.com/sphinx-doc/sphinx.git@master

.travis.yml

@@ -1,11 +1,13 @@
 language: python
 
 env:
-  - SPHINX_VERSION=3.0 TRAVIS_CI=True
+  - SPHINX_VERSION=3.1 TRAVIS_CI=True
 
 python:
   - "3.5"
   - "3.6"
+  - "3.7"
+  - "3.8"
 
 before_install:
   - sudo apt-get update -qq