vspec.py: Specify safe YAML loader, avoids warning
vspec.py: Specify safe YAML loader, avoids warning

This change deals with the warning that was printed before.
(read link for more info):

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

Signed-off-by: Gunnar Andersson <df6c1dc70ee3404c16d7de0a5a8d978b44fa18d4@genivi.org>

GENIVI/vehicle_signal_specification,GENIVI/vehicle_signal_specification