requirements: only list what we really need
Listing all transitive dependencies, including their respective versions
(as done by `pip freeze`, for example) is something which effectively
leads to installing outdated and possibly vulnerable software.
Let's get rid of the transitive dependencies.
Thanks to Esther for noticing.
alabaster==0.7.12
-appdirs==1.4.3
-atomicwrites==1.2.1
-attrs==18.2.0
-Babel==2.6.0
-black==18.9b0
-certifi==2018.10.15
-chardet==3.0.4
-Click==7.0
-cycler==0.10.0
-decorator==4.3.0
-docutils==0.14
-idna==2.7
-imagesize==1.1.0
-Jinja2==2.10
-kiwisolver==1.0.1
-latexcodec==1.0.5
-MarkupSafe==1.0
matplotlib==3.0.0
-more-itertools==4.3.0
networkx==2.3
numpy==1.15.2
-oset==0.1.3
-packaging==18.0
-pluggy==0.7.1
-py==1.7.0
-pybtex==0.21
-pybtex-docutils==0.2.1
Pygments==2.2.0
-pyparsing==2.2.2
pytest==3.8.2
-python-dateutil==2.7.3
-pytz==2018.5
-PyYAML==3.13
-requests==2.19.1
scipy==1.1.0
-six==1.11.0
-snowballstemmer==1.2.1
Sphinx==1.8.1
sphinxcontrib-bibtex==0.4.0
-sphinxcontrib-websupport==1.1.0
-toml==0.10.0
-urllib3==1.23
xlrd==1.2.0
