Fix response ci header (#1244)

* add unit tests, which should fail

* fix CIDict

* moving CIDict to avoid circular imports

* fix unit tests

* use multidict for headers

* fix cookie

* add version constraint for multidict

* omit test coverage for __main__.py

* make flake8 happy

* consolidate check in for loop

* travisci retry build

.coveragerc

@@ -1,7 +1,7 @@
 [run]
 branch = True
 source = sanic
-omit = site-packages, sanic/utils.py
+omit = site-packages, sanic/utils.py, sanic/__main__.py
 
 [html]
 directory = coverage