title: Upgrade to Django 2.2: AttributeError: module 'statistics' has no attribute 'pstdev'
body: <p>Current setup:</p>
  
  <p>Python 3.6</p>
  
  <pre><code>Django==2.2
  gunicorn==19.1.0
  coverage==4.4.1
  django-suit==0.2.26
  django-extensions==2.0.6
  djangorestframework==3.8.2
  djangorestframework-datatables==0.3.0
  djangorestframework-csv==2.1.0
  coreapi==2.3.3
  Faker==0.9.0
  pillow==5.2.0
  simple-crypt==4.1.7
  xlrd==1.1.0
  django-crequest==2018.5.11
  gitpython==2.1.11
  django_icons==0.2.1
  </code></pre>
  
  <p>Upgraded Django from 1.11 to 2.2. After cleaning up some obvious stuff as described in various upgrade checklists, got stuck on this one which does not seem to be answered anywhere. Migration chokes on some "statistics" module. Probably some dependent module is not compatible anymore with upgraded Django:</p>
  
  <p>Trying:</p>
  
  <pre><code>&gt; python manage.py runserver
  </code></pre>
  
  <p>Getting:</p>
  
  <pre><code>File "/Users/myuser/.local/lib/python3.5/site-packages/django/db/backends/sqlite3/base.py", line 230, in get_new_connection
      conn.create_aggregate('STDDEV_POP', 1, list_aggregate(statistics.pstdev))
  AttributeError: module 'statistics' has no attribute 'pstdev'
  </code></pre>
  
  <p>The full traceback:</p>
  
  <pre><code>Exception in thread Thread-1:
  Traceback (most recent call last):
    File "/Users/myuser/miniconda3/lib/python3.5/threading.py", line 914, in _bootstrap_inner
      self.run()
    File "/Users/myuser/miniconda3/lib/python3.5/threading.py", line 862, in run
      self._target(*self._args, **self._kwargs)
    File "/Users/myuser/.local/lib/python3.5/site-packages/django/utils/autoreload.py", line 54, in wrapper
      fn(*args, **kwargs)
    File "/Users/myuser/.local/lib/python3.5/site-packages/django/core/management/commands/runserver.py", line 120, in inner_run
      self.check_migrations()
    File "/Users/myuser/.local/lib/python3.5/site-packages/django/core/management/base.py", line 453, in check_migrations
      executor = MigrationExecutor(connections[DEFAULT_DB_ALIAS])
    File "/Users/myuser/.local/lib/python3.5/site-packages/django/db/migrations/executor.py", line 18, in __init__
      self.loader = MigrationLoader(self.connection)
    File "/Users/myuser/.local/lib/python3.5/site-packages/django/db/migrations/loader.py", line 49, in __init__
      self.build_graph()
    File "/Users/myuser/.local/lib/python3.5/site-packages/django/db/migrations/loader.py", line 212, in build_graph
      self.applied_migrations = recorder.applied_migrations()
    File "/Users/myuser/.local/lib/python3.5/site-packages/django/db/migrations/recorder.py", line 73, in applied_migrations
      if self.has_table():
    File "/Users/myuser/.local/lib/python3.5/site-packages/django/db/migrations/recorder.py", line 56, in has_table
      return self.Migration._meta.db_table in self.connection.introspection.table_names(self.connection.cursor())
    File "/Users/myuser/.local/lib/python3.5/site-packages/django/db/backends/base/base.py", line 256, in cursor
      return self._cursor()
    File "/Users/myuser/.local/lib/python3.5/site-packages/django/db/backends/base/base.py", line 233, in _cursor
      self.ensure_connection()
    File "/Users/myuser/.local/lib/python3.5/site-packages/django/db/backends/base/base.py", line 217, in ensure_connection
      self.connect()
    File "/Users/myuser/.local/lib/python3.5/site-packages/django/db/backends/base/base.py", line 195, in connect
      self.connection = self.get_new_connection(conn_params)
    File "/Users/myuser/.local/lib/python3.5/site-packages/django/db/backends/sqlite3/base.py", line 230, in get_new_connection
      conn.create_aggregate('STDDEV_POP', 1, list_aggregate(statistics.pstdev))
  AttributeError: module 'statistics' has no attribute 'pstdev'
  </code></pre>
  
  <p>Thank you for suggestions.</p>