Traceback on exit with py36

Steps to reproduce:
1. Activate songusage plugin
2. Song song live.
3. Exit OpenLP.

Confirmed on 2.4.4 and trunk

Python: 3.6.0
PyQt5 5.7.1
sqlalchemy 1.1.5
alembic 0.8.10

I tried to delete the songusage db, but it didn't help.

Traceback (most recent call last):
  File "/usr/lib/python3.6/site-packages/sqlalchemy/engine/base.py", line 1182, in _execute_context
    context)
  File "/usr/lib/python3.6/site-packages/sqlalchemy/engine/default.py", line 470, in do_execute
    cursor.execute(statement, parameters)
sqlite3.OperationalError: cannot VACUUM from within a transaction

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/home/tgc/projects/OpenLP/code/trunk-2.4/openlp/core/ui/mainwindow.py", line 1106, in closeEvent
    self.clean_up()
  File "/home/tgc/projects/OpenLP/code/trunk-2.4/openlp/core/ui/mainwindow.py", line 1128, in clean_up
    self.plugin_manager.finalise_plugins()
  File "/home/tgc/projects/OpenLP/code/trunk-2.4/openlp/core/common/openlpmixin.py", line 58, in wrapped
    raise e
  File "/home/tgc/projects/OpenLP/code/trunk-2.4/openlp/core/common/openlpmixin.py", line 54, in wrapped
    return func(*args, **kwargs)
  File "/home/tgc/projects/OpenLP/code/trunk-2.4/openlp/core/lib/pluginmanager.py", line 189, in finalise_plugins
    plugin.finalise()
  File "/home/tgc/projects/OpenLP/code/trunk-2.4/openlp/plugins/songusage/songusageplugin.py", line 146, in finalise
    self.manager.finalise()
  File "/home/tgc/projects/OpenLP/code/trunk-2.4/openlp/core/lib/db.py", line 477, in finalise
    engine.execute("vacuum")
  File "/usr/lib/python3.6/site-packages/sqlalchemy/engine/base.py", line 2055, in execute
    return connection.execute(statement, *multiparams, **params)
  File "/usr/lib/python3.6/site-packages/sqlalchemy/engine/base.py", line 939, in execute
    return self._execute_text(object, multiparams, params)
  File "/usr/lib/python3.6/site-packages/sqlalchemy/engine/base.py", line 1097, in _execute_text
    statement, parameters
  File "/usr/lib/python3.6/site-packages/sqlalchemy/engine/base.py", line 1189, in _execute_context
    context)
  File "/usr/lib/python3.6/site-packages/sqlalchemy/engine/base.py", line 1393, in _handle_dbapi_exception
    exc_info
  File "/usr/lib/python3.6/site-packages/sqlalchemy/util/compat.py", line 203, in raise_from_cause
    reraise(type(exception), exception, tb=exc_tb, cause=cause)
  File "/usr/lib/python3.6/site-packages/sqlalchemy/util/compat.py", line 186, in reraise
    raise value.with_traceback(tb)
  File "/usr/lib/python3.6/site-packages/sqlalchemy/engine/base.py", line 1182, in _execute_context
    context)
  File "/usr/lib/python3.6/site-packages/sqlalchemy/engine/default.py", line 470, in do_execute
    cursor.execute(statement, parameters)
sqlalchemy.exc.OperationalError: (sqlite3.OperationalError) cannot VACUUM from within a transaction [SQL: 'vacuum']