gitignore: Ignore vim temp files.
gitignore: Ignore vim temp files.

BUG=None
TEST=`git status` after opening .gitignore in vim shows .swp before
change but not after change.

Change-Id: I91d0a98b008b7760221d6ae5276a3f69d18e2d61
Reviewed-on: https://gerrit.chromium.org/gerrit/46797
Commit-Queue: Matt Tennant <46e612415b446ccde19638e4035892001c237942@chromium.org>
Reviewed-by: Matt Tennant <46e612415b446ccde19638e4035892001c237942@chromium.org>
Tested-by: Matt Tennant <46e612415b446ccde19638e4035892001c237942@chromium.org>
Reviewed-by: David James <f231dc574bbeb62604660cbc162d1b8642a0a3af@chromium.org>

bpsinc-native/src_third_party_chromite,bpsinc-native/src_third_party_chromite,chadversary/chromiumos.chromite,chadversary/chromiumos.chromite,bpsinc-native/src_third_party_chromite