Fix failing tests (#136)

Author: soxofaan

.github/workflows/test.yml

@@ -36,7 +36,7 @@ jobs:
       run: |
         python -m pip install --upgrade pip
         pip --version
-        pip install -U -r requirements-dev.txt
+        pip install -U pytest pytest-cov
         pip freeze
 
     - name: Build package

requirements.txt

@@ -1,3 +1,5 @@
 pelican>=4
 nbconvert>=5,<6
-markdown
+markdown<3.4
+jinja2<3.1
+nbformat<5.2.0