rename 'isort' to 'check_isort' as requested

.travis.yml

@@ -24,7 +24,7 @@ matrix:
     env: TOX_ENV=py36
 
   - python: 3.6
-    env: TOX_ENV=isort
+    env: TOX_ENV=check_isort
 
   - python: 3.6
     env: TOX_ENV=check-newsfragment

tox.ini

 [tox]
-envlist = packaging, py27, py36, pep8, isort
+envlist = packaging, py27, py36, pep8, check_isort
 
 [testenv]
 deps =
@@ -103,7 +103,7 @@ deps =
     flake8
 commands = /bin/sh -c "flake8 synapse tests {env:PEP8SUFFIX:}"
 
-[testenv:isort]
+[testenv:check_isort]
 skip_install = True
 deps = isort
 commands = /bin/sh -c "isort -c -sp setup.cfg -rc synapse tests"