Authorization header is not masked (regression)

[alextatarinov]

bb4df5b Introduced a regression of #375.
Although request.headers[KEY] lookup is case-insensitive, iterating over .items() yields header keys with the original letter case. The tests pass because they use a lowercased authorization header.
The fix could be as simple as adding k.lower().

django-silk/silk/model_factory.py

Lines 72 to 74 in 274898f

	for k, v in self.request.headers.items():
	if k in sensitive_headers:
	v = RequestModelFactory.CLEANSED_SUBSTITUTE