Bump doc requirements (via pip-compile)

Author: Julian

docs/requirements.in

@@ -0,0 +1,3 @@
+lxml
+sphinx
+sphinxcontrib-spelling

docs/requirements.txt

@@ -1,29 +1,36 @@
-alabaster==0.7.12
-attrs==19.1.0
-Babel==2.7.0
-certifi==2019.6.16
-chardet==3.0.4
-docutils==0.15.2
-greenlet==0.4.13
-idna==2.8
-imagesize==1.1.0
-Jinja2==2.10.1
-lxml==4.4.0
-MarkupSafe==1.1.1
-packaging==19.1
-pyenchant==2.0.0
-Pygments==2.4.2
-pyparsing==2.4.2
-pytz==2019.2
-requests==2.22.0
-six==1.12.0
-snowballstemmer==1.9.0
-Sphinx==2.1.2
-sphinxcontrib-applehelp==1.0.1
-sphinxcontrib-devhelp==1.0.1
-sphinxcontrib-htmlhelp==1.0.2
-sphinxcontrib-jsmath==1.0.1
-sphinxcontrib-qthelp==1.0.2
-sphinxcontrib-serializinghtml==1.1.3
+#
+# This file is autogenerated by pip-compile
+# To update, run:
+#
+#    pip-compile requirements.in
+#
+alabaster==0.7.12         # via sphinx
+babel==2.7.0              # via sphinx
+certifi==2019.9.11        # via requests
+chardet==3.0.4            # via requests
+docutils==0.15.2          # via sphinx
+idna==2.8                 # via requests
+imagesize==1.1.0          # via sphinx
+jinja2==2.10.3            # via sphinx
+lxml==4.4.1
+markupsafe==1.1.1         # via jinja2
+packaging==19.2           # via sphinx
+pyenchant==2.0.0          # via sphinxcontrib-spelling
+pygments==2.4.2           # via sphinx
+pyparsing==2.4.4          # via packaging
+pytz==2019.3              # via babel
+requests==2.22.0          # via sphinx
+six==1.13.0               # via packaging, sphinxcontrib-spelling
+snowballstemmer==2.0.0    # via sphinx
+sphinx==2.2.1
+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
 sphinxcontrib-spelling==4.3.0
-urllib3==1.25.3
+urllib3==1.25.6           # via requests
+
+# The following packages are considered to be unsafe in a requirements file:
+# setuptools==41.6.0        # via sphinx