Fix expiry check due to future deprication

Author: artemlos

licensing/models.py

@@ -140,7 +140,7 @@ def load_from_string(rsa_pub_key, string, signature_expiration_interval = -1):
                     licenseKey = LicenseKey.from_response(response)
 
                     if signature_expiration_interval > 0 and \
-                    (licenseKey.sign_date + datetime.timedelta(days=1*signature_expiration_interval) < datetime.datetime.utcnow()):
+                    (licenseKey.sign_date + datetime.timedelta(days=1*signature_expiration_interval) < datetime.datetime.now(dateime.timezone.utc)):
                         return None
 
                     return licenseKey