fix url.parse tests for Python 3.6

This is a simpler version of @Kriechi's patch.

test/mitmproxy/net/http/test_url.py

@@ -1,3 +1,6 @@
+import pytest
+import sys
+
 from mitmproxy.test import tutils
 from mitmproxy.net.http import url
 
@@ -42,14 +45,18 @@ def test_parse():
     # Null byte in host
     with tutils.raises(ValueError):
         url.parse("http://foo\0")
-    # Port out of range
-    _, _, port, _ = url.parse("http://foo:999999")
-    assert port == 80
     # Invalid IPv6 URL - see http://www.ietf.org/rfc/rfc2732.txt
     with tutils.raises(ValueError):
         url.parse('http://lo[calhost')
 
 
+@pytest.mark.skipif(sys.version_info < (3, 6), reason='requires Python 3.6 or higher')
+def test_parse_port_range():
+    # Port out of range
+    with tutils.raises(ValueError):
+        url.parse("http://foo:999999")
+
+
 def test_unparse():
     assert url.unparse("http", "foo.com", 99, "") == "http://foo.com:99"
     assert url.unparse("http", "foo.com", 80, "/bar") == "http://foo.com/bar"