BUGFIX: Skipping headers correctly

Headers in `IGNORED_HEADERS` were not skipped as the comparison was case sensitive while it should not.

django_seo_js/backends/base.py

@@ -63,7 +63,7 @@ def __init__(self, *args, **kwargs):
     def build_django_response_from_requests_response(self, response):
         r = HttpResponse(response.content)
         for k, v in response.headers.items():
-            if k not in IGNORED_HEADERS:
+            if k.lower() not in IGNORED_HEADERS:
                 r[k] = v
         r['content-length'] = len(response.content)
         r.status_code = response.status_code