mypy: Update to 0.630 and pin that version

.travis.yml

@@ -48,7 +48,7 @@ install:
     # version supported. But Python 3.7 requires slower-to-start VMs,
     # so we run it on 3.6 to minimize total CI run time.
     - if [[ $TRAVIS_PYTHON_VERSION == '3.6' ]]; then travis_retry pip install -r docs/requirements.txt; fi
-    - if [[ $TRAVIS_PYTHON_VERSION == '3.6' ]]; then travis_retry pip install flake8 mypy; fi
+    - if [[ $TRAVIS_PYTHON_VERSION == '3.6' ]]; then travis_retry pip install flake8 mypy==0.630; fi
     # On travis the extension should always be built
     - if [[ $TRAVIS_PYTHON_VERSION != 'pypy'* ]]; then export TORNADO_EXTENSION=1; fi
     - travis_retry python setup.py install

tornado/wsgi.py

@@ -93,13 +93,13 @@ def __call__(self, request: httputil.HTTPServerRequest) -> None:
         response = []  # type: List[bytes]
 
         def start_response(
-                status: str, response_headers: List[Tuple[str, str]],
+                status: str, headers: List[Tuple[str, str]],
                 exc_info: Optional[Tuple[Optional[Type[BaseException]],
                                          Optional[BaseException],
                                          Optional[TracebackType]]]=None
         ) -> Callable[[bytes], Any]:
             data["status"] = status
-            data["headers"] = response_headers
+            data["headers"] = headers
             return response.append
         app_response = self.wsgi_application(
             WSGIContainer.environ(request), start_response)

tox.ini

@@ -129,4 +129,4 @@ changedir = {toxinidir}
 [testenv:py3-mypy]
 commands = mypy {posargs:tornado}
 changedir = {toxinidir}
-deps = mypy
+deps = mypy==0.630