Update changelog/153.bugfix.rst
removing implementation detail from changelog
Exit program (``python -m rasa_sdk --actions actions`` or
``rasa run actions --actions actions``) if a requested module under the
-``--actions`` command-line option cannot be found,
-by adding sys.exit(1) after Import Error in in register_package() function in executer.py
+``--actions`` command-line option cannot be found.
