Update ModelBase.py (#283)

Typo: 'NotImplementeError' --> 'NotImplementedError'

models/ModelBase.py

@@ -279,7 +279,7 @@ class ModelBase(object):
 
     #overridable
     def get_converter(self):
-        raise NotImplementeError
+        raise NotImplementedError
         #return existing or your own converter which derived from base
 
     def get_target_iter(self):