Update requirements.

requirements.txt

@@ -2,37 +2,39 @@
 # This file is autogenerated by pip-compile
 # To update, run:
 #
-#    pip-compile --output-file requirements.txt requirements.in
+#    pip-compile -U
 #
---index-url https://pypi.python.org/simple
-
 alabaster==0.7.12         # via sphinx
 babel==2.6.0              # via sphinx
-certifi==2018.11.29       # via requests
+certifi==2019.3.9         # via requests
 chardet==3.0.4            # via requests
-colorama==0.4.1           # via sphinx
 commonmark==0.8.1         # via recommonmark
 docutils==0.14            # via recommonmark, sphinx
 filelock==3.0.10          # via tox
 future==0.17.1            # via commonmark
 idna==2.8                 # via requests
 imagesize==1.1.0          # via sphinx
-jinja2==2.10              # via sphinx
-markupsafe==1.1.0         # via jinja2
+jinja2==2.10.1            # via sphinx
+markupsafe==1.1.1         # via jinja2
 packaging==19.0           # via sphinx
-pluggy==0.8.1             # via tox
-py==1.7.0                 # via tox
+pluggy==0.9.0             # via tox
+py==1.8.0                 # via tox
 pygments==2.3.1           # via sphinx
-pyparsing==2.3.1          # via packaging
-pytz==2018.9              # via babel
+pyparsing==2.4.0          # via packaging
+pytz==2019.1              # via babel
 recommonmark==0.5.0
 requests==2.21.0          # via sphinx
-six==1.12.0               # via packaging, sphinx, tox
+six==1.12.0               # via packaging, tox
 snowballstemmer==1.2.1    # via sphinx
 sphinx-rtd-theme==0.4.3
-sphinx==1.8.4
-sphinxcontrib-websupport==1.1.0  # via sphinx
+sphinx==2.0.1
+sphinxcontrib-applehelp==1.0.1  # via sphinx
+sphinxcontrib-devhelp==1.0.1  # via sphinx
+sphinxcontrib-htmlhelp==1.0.2  # via sphinx
+sphinxcontrib-jsmath==1.0.1  # via sphinx
+sphinxcontrib-qthelp==1.0.2  # via sphinx
+sphinxcontrib-serializinghtml==1.1.3  # via sphinx
 toml==0.10.0              # via tox
-tox==3.7.0
-urllib3==1.24.1           # via requests
-virtualenv==16.4.0        # via tox
+tox==3.9.0
+urllib3==1.24.2           # via requests
+virtualenv==16.4.3        # via tox