Update NEWS.txt

NEWS.txt

@@ -16,6 +16,9 @@ Bug fixes
    in all case as well as inc_subtensor(*, *).
    Note2: If your code have this behavior, we print a warning by default.
    (Frederic B.)
+ * Fixed an issue whereby config values were used as default arguments,
+   with those defaults then stuck at old values if the config variables were
+   changed during program execution. (David W-F)
 
 Documentation
  * Added in the tutorial documentation on how to extend Theano.