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

Change-Id: I101fa672600413c7aa1e2e8a8c617b3d4757aede
MultiPart: 19/28
PresubmitTest: none
diff --git a/.gitignore b/.gitignore
index 63ec737..751fd3e 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,3 +1,5 @@
+/.jiri
+#TODO(nlacasse): Get rid of .v23 below once v23->jiri transition is complete.
 /.v23
 
 # Don’t commit the following directories created by pub.