Freeze requirements

requirements.txt

-sphinx-rtd-theme
-nbsphinx
+alabaster==0.7.12
+async-generator==1.10
+attrs==20.2.0
+Babel==2.8.0
+bleach==3.2.1
+certifi==2020.6.20
+chardet==3.0.4
+defusedxml==0.6.0
+docutils==0.16
+entrypoints==0.3
+idna==2.10
+imagesize==1.2.0
+ipython-genutils==0.2.0
+Jinja2==2.11.2
+jsonschema==3.2.0
+jupyter-client==6.1.7
+jupyter-core==4.6.3
+jupyterlab-pygments==0.1.2
+MarkupSafe==1.1.1
+mistune==0.8.4
+nbclient==0.5.1
+nbconvert==6.0.7
+nbformat==5.0.8
+nbsphinx==0.8.0
+nest-asyncio==1.4.1
+packaging==20.4
+pandocfilters==1.4.2
+Pygments==2.7.1
+pyparsing==2.4.7
+pyrsistent==0.17.3
+python-dateutil==2.8.1
+pytz==2020.1
+pyzmq==19.0.2
+requests==2.24.0
+six==1.15.0
+snowballstemmer==2.0.0
+Sphinx==3.2.1
+sphinx-rtd-theme==0.5.0
+sphinxcontrib-applehelp==1.0.2
+sphinxcontrib-devhelp==1.0.2
+sphinxcontrib-htmlhelp==1.0.3
+sphinxcontrib-jsmath==1.0.1
+sphinxcontrib-qthelp==1.0.3
+sphinxcontrib-serializinghtml==1.1.4
+testpath==0.4.4
+tornado==6.0.4
+traitlets==5.0.5
+urllib3==1.25.11
+webencodings==0.5.1