Update Sphinx to version 1.8.5 (Graylog2#602)

Updating a local development environment can be done with:

    pip install -r requirements.txt --upgrade

requirements.txt

@@ -1,24 +1,33 @@
-alabaster==0.7.7
-argh==0.26.1
-Babel==2.3.4
-backports-abc==0.4
-backports.ssl-match-hostname==3.5.0.1
-certifi==2016.2.28
-docutils==0.12
-imagesize==0.7.1
-Jinja2==2.8
-livereload==2.4.1
-MarkupSafe==0.23
+alabaster==0.7.12
+argh==0.26.2
+Babel==2.6.0
+backports-abc==0.5
+backports.ssl-match-hostname==3.7.0.1
+certifi==2019.3.9
+chardet==3.0.4
+docutils==0.14
+futures==3.2.0
+idna==2.8
+imagesize==1.1.0
+Jinja2==2.10
+livereload==2.6.0
+MarkupSafe==1.1.1
+packaging==19.0
 pathtools==0.1.2
 port-for==0.3.1
-Pygments==2.1.3
-pytz==2016.4
-PyYAML==3.11
+Pygments==2.3.1
+pyparsing==2.3.1
+pytz==2018.9
+PyYAML==5.1
+requests==2.21.0
 singledispatch==3.4.0.3
-six==1.10.0
+six==1.12.0
 snowballstemmer==1.2.1
-Sphinx==1.4.1
-sphinx-autobuild==0.6.0
-sphinx-rtd-theme==0.1.9
-tornado==4.3
-watchdog==0.8.3
+Sphinx==1.8.5
+sphinx-autobuild==0.7.1
+sphinx-rtd-theme==0.4.3
+sphinxcontrib-websupport==1.1.0
+tornado==5.1.1
+typing==3.6.6
+urllib3==1.24.1
+watchdog==0.9.0