Update app.py

app.py

@@ -18,7 +18,7 @@ def my_custom_tool(arg1:str, arg2:int)-> str: #it's import to specify the return
     """
     if arg2 == 'first':
         return arg1[0]
-    else if arg2 == 'last':
+    elif arg2 == 'last':
         return arg1[-1]
     else:
         return 'arg2 format is not correct'