Remove "permanent" from the kind of disallowed changes.

Author: jyasskin

index.bs

@@ -80,7 +80,7 @@ and embodied in the various standards that user agents implement.
 
 [[design-principles#safe-to-browse|It should be safe to visit a web page.]]
 That is, simply visiting a page must not allow
-the page to make permanent changes to the user's computer or environment
+the page to make changes to the user's computer or environment
 (for example by installing malware),
 and simply visiting should reveal
 as little information as practical about the user to the page,