Bump pytest to 5.4.0 to resolve version conflicts (#190)

Author: tarikki

setup.py

@@ -10,7 +10,7 @@
 crypto_requires = ["cryptography>=1.3.0"]
 
 test_requires = crypto_requires + [
-    "pytest~=3.6.0",
+    "pytest~=5.4.0",
     "pytest-asyncio~=0.8",
     "async_generator~=1.8",
     "async-timeout~=2.0",