Fix tox config to install latest pip packages

Trial changed command in latest versions of twisted

.travis.yml

@@ -15,7 +15,7 @@ before_install:
 install:
   - bash -c "echo $APTPACKAGES"
   - sudo apt-get install $APTPACKAGES
-  - pip install "tox==2.1.1"
+  - pip install tox
 
 env:
   global:

tox.ini

@@ -16,11 +16,12 @@ envlist = py27, flake8, docs, pylint
 minversion=1.8
 
 [testenv]
-passenv = DISPLAY
+install_command = pip install --ignore-installed {opts} {packages}
+passenv = DISPLAY PYTHONPATH
 setenv = PYTHONPATH = {env:PWD}:
 sitepackages = True
 deps =
-    twisted==16.6
+    twisted[tls]
     service_identity
     mako
     chardet
@@ -58,10 +59,9 @@ commands = py.test -v --basetemp=_pytest_temp -s -m "todo" deluge/tests
 
 [testenv:trial]
 setenv = {[testenv]setenv}:{env:PWD}/deluge/tests
-whitelist_externals = trial
 commands =
     python -c "import libtorrent as lt; print lt.__version__"
-    trial --reporter=deluge-reporter deluge.tests
+    python -m twisted.trial --reporter=deluge-reporter deluge.tests
 
 [testenv:plugins]
 setenv = PYTHONPATH = {env:PWD}:{env:PWD}/deluge/plugins