Fix SnapshotProvider failing depending on python3.7

lib/tfw/components/snapshot_provider.py

@@ -2,7 +2,7 @@
 # All Rights Reserved. See LICENSE file for details.
 
 import re
-from subprocess import run, CalledProcessError
+from subprocess import run, CalledProcessError, PIPE
 from getpass import getuser
 from os.path import isdir
 from datetime import datetime
@@ -87,7 +87,8 @@ class SnapshotProvider:
         ))
 
     def _get_stdout(self, *args, **kwargs):
-        kwargs['capture_output'] = True
+        kwargs['stdout'] = PIPE
+        kwargs['stderr'] = PIPE
         stdout_bytes = self._run(*args, **kwargs).stdout
         return stdout_bytes.decode().rstrip('\n')