Add vim swap files to gitignore

Test: git show while file opened in vim

This keeps "git show" from showing my swap files as untracked files.

Change-Id: I5f17bdbd1fda22823a9356445db5bc4a7dd279d9
diff --git a/.gitignore b/.gitignore
index 45884c4..d7aebc6 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,2 +1,3 @@
 /.idea
 *.iml
+*.sw*