Ignore sub repositories when checking out via repo tool

I'm not sure why the previous .gitignore entry wasn't working. With this
one, macro and helm-repo-tools are effectively ignored.

Change-Id: Ib4720d768c00b34662d569cbce0b4af07fbe1de5
diff --git a/.gitignore b/.gitignore
index 255335d..c96efd1 100644
--- a/.gitignore
+++ b/.gitignore
@@ -5,8 +5,8 @@
 requirements.lock
 
 # child repos (defined in the repo manifest)
-macro/*
-helm-repo-tools/*
+macro/
+helm-repo-tools/
 
 # ignore dependent chart dirs
 charts