adding imports (#23)

Author: fshabashev

mindsdb_sql_parser/ast/mindsdb/__init__.py

@@ -15,7 +15,7 @@
 from .drop_job import DropJob
 from .chatbot import CreateChatBot, UpdateChatBot, DropChatBot
 from .trigger import CreateTrigger, DropTrigger
-from .knowledge_base import CreateKnowledgeBase, DropKnowledgeBase
+from .knowledge_base import CreateKnowledgeBase, DropKnowledgeBase, CreateKnowledgeBaseIndex, DropKnowledgeBaseIndex
 from .skills import CreateSkill, DropSkill, UpdateSkill
 
 # remove it in next release