docs: fix requirements.txt & pin sphinxcontrib-versioning version

docs/requirements.txt

@@ -1,20 +1,30 @@
 alabaster==0.7.12
-Babel==2.6.0
-certifi==2018.10.15
+attrs==19.1.0
+Babel==2.7.0
+certifi==2019.6.16
 chardet==3.0.4
-docutils==0.14
-idna==2.7
+Click==7.0
+colorclass==2.2.0
+docutils==0.15.2
+idna==2.8
 imagesize==1.1.0
-Jinja2==2.10
-MarkupSafe==1.1.0
-packaging==18.0
-Pygments==2.2.0
-pyparsing==2.3.0
-pytz==2018.7
-requests==2.20.1
-six==1.11.0
-snowballstemmer==1.2.1
-Sphinx==1.8.2
-sphinx-rtd-theme==0.4.2
-sphinxcontrib-websupport==1.1.0
-urllib3==1.24.1
+Jinja2==2.10.1
+MarkupSafe==1.1.1
+packaging==19.1
+Pygments==2.4.2
+pyparsing==2.4.2
+pytz==2019.2
+requests==2.22.0
+six==1.12.0
+snowballstemmer==1.9.1
+Sphinx==1.8.5
+sphinx-rtd-theme==0.4.3
+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
+-e git://github.com/rwblair/sphinxcontrib-versioning.git@7e3885a389a809e17ea55261316b7b0e98dbf98f#egg=sphinxcontrib-versioning
+sphinxcontrib-websupport==1.1.2
+urllib3==1.25.3