Issue #16714: use 'raise' exceptions, don't 'throw'.

Patch by Serhiy Storchaka.
diff --git a/Lib/lib-tk/Tkinter.py b/Lib/lib-tk/Tkinter.py
index 4791950..e5c2e51 100644
--- a/Lib/lib-tk/Tkinter.py
+++ b/Lib/lib-tk/Tkinter.py
@@ -155,7 +155,7 @@
     pass
 
 def _exit(code=0):
-    """Internal function. Calling it will throw the exception SystemExit."""
+    """Internal function. Calling it will raise the exception SystemExit."""
     try:
         code = int(code)
     except ValueError: