Update python/examples/7-explore-advanced.py

Co-authored-by: Guillaume Fraux <[email protected]>

python/examples/7-explore-advanced.py

@@ -200,7 +200,7 @@ def mace_mp0_tsne(frames, environments):
 
 def soap_tnse_with_environments(frames, environments):
     if environments is None:
-        raise ValueError("'environments' supposed to be provided")
+        raise ValueError("'environments' must be provided")
 
     grouped_envs = {}
     unique_structures = set()