[backend] fix misspelling "unkown" -> "unknown"

Fixes #190

beat/editor/backend/assetmodel.py

@@ -46,7 +46,7 @@ class AssetType:
 
     @classmethod
     def path(cls, type_):
-        path = "unkown"
+        path = "unknown"
         if type_ == cls.Algorithm:
             path = "algorithms"
         elif type_ == cls.Database: