Tweak .gitignore format for Bazel artifacts.

.gitignore

diff --git a/.gitignore b/.gitignore
index 5ca8068..95ef78e 100644
--- a/.gitignore
+++ b/.gitignore
@@ -17,7 +17,7 @@
 build/
 
 # Bazel artifacts
-bazel-*/
+/bazel-*
 
 # Local-only config options
 user.bazelrc