gitignore: add nano/vim swap file

Ignore swap/lock files.

Git-Dch: Ignore
Signed-off-by: Arturo Borrero Gonzalez <arturo@debian.org>

.gitignore

@@ -22,3 +22,5 @@ Makefile.in
 
 /iptables/xtables-multi
 /iptables/xtables-compat-multi
+
+*.swp