[epiphany] Update TODO

[Michael Catanzaro <mcatanzaro src gnome org>]

commit b9f982637f4bd1b3cf1fd576a05324943f399334
Author: Michael Catanzaro <mcatanzaro igalia com>
Date:   Tue Nov 27 20:13:38 2018 -0600

    Update TODO

 TODO | 1 +
 1 file changed, 1 insertion(+)
---
diff --git a/TODO b/TODO
index e9a262343..e50e31b62 100644
--- a/TODO
+++ b/TODO
@@ -1,5 +1,6 @@
 Some TODO items, in no particular order:
 
+- Remove all use of slice allocator
 - Rename all classes that lack the Ephy namespace
 - Use g_signal_emit instead of g_signal_emit_by_name
 - Use GDK_EVENT_PROPAGATE/GDK_EVENT_STOP.