fix content length mismatch in windows and other platform

The current implementation of `sanic` attempts to make use of `ujson` if
it's available in the system and if not, it will default to the inbuilt
`json` module provided by python.

The current implementation of `ujson` does not provide a mechanism to
provide a custom `seperators` parameter as part of the `dumps` method
invocation and the default behavior of the module is to strip all the
spaces around seperators such as `:` and `,`. This leads to an
inconsistency in the response length when the response is generated
using the `ujson` and in built `json` module provided by python.

To maintain the consistency, this commit overrides the default behavior
of the `dumps` method provided by the `json` module to add a `seperators`
argument that will strip the white spaces around these character like
the default behavior of `ujson`

This addresses the issue referenced in #1398

Signed-off-by: Harsha Narayana <harsha2k4@gmail.com>

sanic/response.py

@@ -1,3 +1,4 @@
+from functools import partial
 from mimetypes import guess_type
 from os import path
 from urllib.parse import quote_plus
@@ -12,7 +13,11 @@ from sanic.helpers import STATUS_CODES, has_message_body, remove_entity_headers
 try:
     from ujson import dumps as json_dumps
 except BaseException:
-    from json import dumps as json_dumps
+    from json import dumps
+
+    # This is done in order to ensure that the JSON response is
+    # kept consistent across both ujson and inbuilt json usage.
+    json_dumps = partial(dumps, separators=(",", ":"))
 
 
 class BaseHTTPResponse: