fix Tornado 5.0 event loop

https://github.com/tornadoweb/tornado/issues/2183#issuecomment-371001254

setup.py

@@ -77,7 +77,7 @@ setup(
         "pyperclip>=1.6.0, <1.7",
         "ruamel.yaml>=0.13.2, <0.16",
         "sortedcontainers>=1.5.4, <1.6",
-        "tornado>=4.3, <4.6",
+        "tornado>=4.3,<5.1",
         "urwid>=2.0.1,<2.1",
         "wsproto>=0.11.0,<0.12.0",
     ],

test/mitmproxy/addons/test_onboarding.py

@@ -4,6 +4,10 @@ from mitmproxy.addons import onboarding
 from mitmproxy.test import taddons
 from .. import tservers
 
+import asyncio
+import tornado.platform.asyncio
+asyncio.set_event_loop_policy(tornado.platform.asyncio.AnyThreadEventLoopPolicy())
+
 
 class TestApp(tservers.HTTPProxyTest):
     def addons(self):