attach type:task label to Sub-tasks (#142)

diff --git a/migration/src/common.py b/migration/src/common.py
index 9f50564..bc74553 100644
--- a/migration/src/common.py
+++ b/migration/src/common.py
@@ -195,7 +195,8 @@
     "Improvement": "type:enhancement",
     "Test": "type:test",
     "Wish": "type:enhancement",
-    "Task": "type:task"
+    "Task": "type:task",
+    "Sub-task": "type:task"
 }