Fix typo.

cml/domain/deconstruction.py

@@ -96,7 +96,7 @@ class RelativeFinder:
 class Deconstructor:
     TIME_COLUMN = "T"
     SUBJECT_COLUMN = "Sigma"
-    PUPORSE_COLUMN = "Z"
+    PURPOSE_COLUMN = "Z"
 
     def __init__(self, knowledge_database, relative_finder, settings):
         self.knowledge_database = knowledge_database