(SIO-2222) Use yaml.safe_load instead of yaml.load

This fixes following warning:
     YAMLLoadWarning: calling yaml.load() without Loader=... is deprecated, as the default Loader is unsafe. Please read https://msg.pyyaml.org/load for full details.

Using yaml.load on user input (uploaded packages) is unsefe.

Change-Id: I3e1c4dbaa7e4342ada4216e46956883aa0edd5a7

oioioi/sinolpack/models.py

@@ -16,7 +16,7 @@ class ExtraConfig(models.Model):
     def parsed_config(self):
         if not self.config:
             return {}
-        return yaml.load(self.config)
+        return yaml.safe_load(self.config)
 
     class Meta(object):
         verbose_name = _("sinolpack's configuration")