TBR: lib: Add '/.jiri' to .gitignore in all repos.

Change-Id: I867e5ec7d4b684abe7ad77344785767518d20cb8
MultiPart: 9/28
PresubmitTest: none
diff --git a/.gitignore b/.gitignore
index 53191fd..5e2e933 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1 +1,3 @@
+/.jiri
+#TODO(nlacasse): Get rid of .v23 below once v23->jiri transition is complete.
 /.v23