typo

--- a/NEWS	Thu Sep 17 12:06:38 2020 +0200
+++ b/NEWS	Thu Sep 17 13:55:21 2020 +0200
@@ -111,7 +111,7 @@
 into its components "drop_bit" and "take_bit".  INCOMPATIBILITY.
 
 * Session HOL-Word: Uniform polymorphic "mask" operation for both
-types int and word.  INCOMPATIBILITY
+types int and word.  INCOMPATIBILITY.
 
 * Session HOL-Word: Operations lsb, msb and set_bit are separated
 into theories Misc_lsb, Misc_msb and Misc_set_bit respectively.