fix(security): Load yaml in safe mode

[germainlefebvre4]

Current status: Yaml configuration file is loaded as raw file.

$ pipenv run bandit -r handler.py

>> Issue: [B506:yaml_load] Use of unsafe yaml load. Allows instantiation of arbitrary objects. Consider yaml.safe_load().
   Severity: Medium   Confidence: High
   Location: handler.py:35
   More Info: https://bandit.readthedocs.io/en/latest/plugins/b506_yaml_load.html
34      with open("/etc/config/ns-killer.conf", 'r') as ymlfile:
35          cfg = yaml.load(ymlfile, Loader=yaml.FullLoader)

Solution:

• Enable safe_mode in yaml loader