livereload server not start without "--ignore-file-extensions" option

[ghost]

Hi, thanks to good app.
I found a little bug as below. (with this master branch)

when you do this command, it's ok.
python manage.py livereload --ignore-file-extensions=.less,.scss

but do this, error occur.
python manage.py livereload

i think this is cause from this code in livereload.py.
options.get('ignore_file_extensions', '').split(',')

error message

Traceback (most recent call last):
  File "manage.py", line 15, in <module>
    execute_from_command_line(sys.argv)
  File "/usr/local/lib/python3.7/site-packages/django/core/management/__init__.py", line 381, in execute_from_command_line
    utility.execute()
  File "/usr/local/lib/python3.7/site-packages/django/core/management/__init__.py", line 375, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/usr/local/lib/python3.7/site-packages/django/core/management/base.py", line 316, in run_from_argv
    self.execute(*args, **cmd_options)
  File "/usr/local/lib/python3.7/site-packages/django/core/management/base.py", line 353, in execute
    output = self.handle(*args, **options)
  File "/usr/local/lib/python3.7/site-packages/livereload/management/commands/livereload.py", line 62, in handle
    ignore_file_extensions = options.get('ignore_file_extensions', '').split(',')
AttributeError: 'NoneType' object has no attribute 'split'