un-pin Twisted, require autobahn >=0.14.1

The new autobahn release removes the Twisted pin, so we no longer need
one. Depend on the new autobahn to flush out any environments that are
still using the old one (and thus can't use the current Twisted).

Thanks https://github.com/crossbario/autobahn-python/issues/680 !

setup.py

@@ -25,8 +25,8 @@ setup(name="magic-wormhole",
                      ]},
       install_requires=["spake2==0.7", "pynacl", "argparse",
                         "six",
-                        "twisted==16.1.1", # since autobahn pins it
-                        "autobahn[twisted]",
+                        "twisted",
+                        "autobahn[twisted] >= 0.14.1",
                         "hkdf", "tqdm",
                         ],
       extras_require={"tor": ["txtorcon", "ipaddr"]},