Fix the example crashing

[Innoviox]

Based on the instructions in the readme, the example crashed with the following error:

Traceback (most recent call last):
  File "/Users/simonchervenak/Documents/GitHub/structural-probes/structural-probes/run_demo.py", line 174, in <module>
    yaml_args= yaml.load(open(cli_args.experiment_config))
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
TypeError: load() missing 1 required positional argument: 'Loader'

I updated the code to use safe_load to fix this error.