Fixed typo in context.unset_data

Picked from 71e5c5b and 38029e3

src/formatitko/context.py

@@ -143,8 +143,8 @@ class Context:
 
 	def unset_data(self, key: str):
 		if key == "":
-			self._doc = {}
+			self._data = {}
-		data = self._doc
+		data = self._data
 		keys = key.split(".")
 		for k in keys[:-1]:
 			data = data[k]