Add safe mode argument to open() function for credential_path

[hacktobeer]

dftimewolf/dftimewolf/lib/processors/turbinia_base.py

Line 274 in e83e308

with open(credentials_path, 'w', encoding='utf-8') as token:

Adding a mode argument to the open() call will make sure the credential file is created with safe(r) permissions depending on umask os settings. Without the mode argument the credential file could be created world readable.