Update required for init_app method

[SlimBeji]

Hello,

I am trying to use flask-wdb via the pattern

wdb = Wdb()
wdb.init_app(app)

I am getting this error
File "/usr/local/lib/python3.8/site-packages/flask_wdb.py", line 18, in init_app
app.wsgi_app = WdbMiddleware(app.wsgi_app, start_disabled, theme)
TypeError: init() takes from 2 to 3 positional arguments but 4 were given

I think a little update is needed.