[requires.io] dependency update

Author: requires

tox.ini

@@ -18,7 +18,7 @@ commands = flake8 --max-complexity 10 h2 test
 
 [testenv:docs]
 basepython=python3.7
-deps = sphinx==1.4.9
+deps = sphinx==2.2.0
 changedir = {toxinidir}/docs
 whitelist_externals = rm
 commands =
@@ -27,7 +27,7 @@ commands =
 
 [testenv:graphs]
 basepython=python2.7
-deps = graphviz==0.11.1
+deps = graphviz==0.12
 commands =
     python visualizer/visualize.py -i docs/source/_static
 
@@ -42,7 +42,7 @@ commands =
 
 [testenv:h2spec]
 basepython=python3.6
-deps = twisted[tls]==17.1.0
+deps = twisted[tls]==19.7.0
 whitelist_externals = {toxinidir}/test/h2spectest.sh
 commands =
     {toxinidir}/test/h2spectest.sh