Ignore vim .swp files.

BUG=None
TEST=do a 'git add' while editing a file with vim

Change-Id: I8137368083bca10c672b5c0b3cdc085603568b2b
Reviewed-on: https://gerrit.chromium.org/gerrit/43080
Commit-Queue: Richard Barnette <jrbarnette@chromium.org>
Tested-by: Richard Barnette <jrbarnette@chromium.org>
Reviewed-by: Scott Zawalski <scottz@chromium.org>
diff --git a/.gitignore b/.gitignore
index bcb0c16..c65bc98 100644
--- a/.gitignore
+++ b/.gitignore
@@ -26,6 +26,7 @@
 *.rej
 .*~
 *~
+.*.swp
 .#*
 .DS_Store.
 # additional patterns: