Issue in app/create_app.py

[Kentoseth]

On a Linux machine, I get this error:

Traceback (most recent call last):
  File "manage.py", line 7, in <module>
    app = create_app()
  File "../Flask-User-starter-app/app/create_app.py", line 24, in create_app
    app.config.from_pyfile(env_settings_file)
  File "../lib/python3.4/site-packages/flask/config.py", line 129, in from_pyfile
    with open(filename) as config_file:
FileNotFoundError: [Errno 2] Unable to load configuration file (No such file or directory): '../Flask-User-starter-app/appenv_settings.py'

The issue is in create_app.py on line 21:

default_filename = app.root_path + 'env_settings.py'

Which can be fixed with:

default_filename = app.root_path + '/env_settings.py'

I have not opened a PR for this because it may break non-Linux installs by creating // for the file-path.

Please confirm, otherwise I will open a PR for it.