* test/automated/flymake/warnpred/test.pl: Tweak format

The previous format seems to have stopped giving a warning with perl 5.20.1,
for some reason.

test/ChangeLog

+2014-12-13  Glenn Morris  <rgm@gnu.org>
+
+	* automated/flymake/warnpred/test.pl: Tweak format, since the
+	previous one seems to have stopped giving a warning with perl 5.20.1.
+
 2014-11-22  Fabián Ezequiel Gallina  <fgallina@gnu.org>
 
 	* automated/python-tests.el

test/automated/flymake/warnpred/test.pl

 @arr = [1,2,3,4];
-@arr[1] = -1;
+$b = @arr[1];