Support overriding default exception reporter

As of Django 3.1 it is possible to override which exception report to
use:
https://docs.djangoproject.com/en/4.1/releases/3.1/#error-reporting

Relevant issue:
#100

django_slack/log.py

@@ -2,7 +2,7 @@
 import logging
 
 from django.conf import settings
-from django.views.debug import ExceptionReporter
+from django.views.debug import get_exception_reporter_class
 
 from . import slack_message
 
@@ -49,7 +49,7 @@ def emit(self, record):
         else:
             exc_info = (None, record.getMessage(), None)
 
-        reporter = ExceptionReporter(request, is_email=True, *exc_info)
+        reporter = get_exception_reporter_class(request)(request, is_email=True, *exc_info)
 
         try:
             tb = reporter.get_traceback_text()