fix if statement for RECAPTCHA DISABLED

Author: MarekOMilo

snowpenguin/django/recaptcha3/fields.py

@@ -15,7 +15,7 @@
 
 class ReCaptchaField(forms.CharField):
     def __init__(self, attrs=None, *args, **kwargs):
-        if os.environ.get('RECAPTCHA_DISABLE', None) is not None:
+        if os.environ.get('RECAPTCHA_DISABLE', None) is None:
             self._private_key = kwargs.pop('private_key', settings.RECAPTCHA_PRIVATE_KEY)
             self._score_threshold = kwargs.pop('score_threshold', settings.RECAPTCHA_SCORE_THRESHOLD)