find_stray_empty_lines: fix tail "invalid context" error

"tail -1" works only with one input file. Using it with multiple input
files throws following error on Ubuntu systems:

tail: option used in invalid context

Adding "-n" makes it work on all cases.

Signed-off-by: Javier Viguera <javier.viguera@digi.com>
Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>
1 file changed