bump dev dependencies

Author: Kriechi

tox.ini

@@ -12,9 +12,9 @@ python =
 passenv =
     GITHUB_*
 deps =
-    pytest==5.4.3
-    pytest-cov==2.10.0
-    pytest-xdist==1.33.0
+    pytest==6.0.1
+    pytest-cov==2.10.1
+    pytest-xdist==2.0.0
 commands =
     pytest --cov-report=xml --cov-report=term --cov=wsproto {posargs}
 
@@ -31,7 +31,7 @@ commands =
 basepython = python3.8
 deps =
     black==19.10b0
-    isort==5.0.3
+    isort==5.4.2
 commands =
     black --check --diff src/ test/ example/ compliance/
     isort --check --diff src/ test/ example/ compliance/
@@ -52,7 +52,7 @@ commands = prospector
 [testenv:docs]
 basepython = python3.8
 deps =
-    sphinx==3.1.2
+    sphinx==3.2.1
 whitelist_externals = make
 changedir = {toxinidir}/docs
 commands =