Merge pull request #127 from kutaslab/docs

Restrict nbconvert version to avoid version 5.4

.travis.yml

@@ -18,7 +18,7 @@ script:
 after_success:
     - pip install codecov && codecov
 before_deploy:
-    - pip install sphinx sphinx_rtd_theme jupyter nbsphinx
+    - pip install sphinx sphinx_rtd_theme jupyter nbsphinx nbconvert!=5.4
     - conda install -c conda-forge pandoc
     - pip install -e . # install fitgrid locally so it can be imported in the notebook
     - conda list