website: update .gitignore

Signed-off-by: Masanori Ogino <masanori.ogino@gmail.com>
Change-Id: I8f299a4d65be6105d228573a1075e14ca3fc6122
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5-website/+/55843
Reviewed-by: Bobby Bruce <bbruce@ucdavis.edu>
Maintainer: Bobby Bruce <bbruce@ucdavis.edu>
Tested-by: Bobby Bruce <bbruce@ucdavis.edu>
diff --git a/.gitignore b/.gitignore
index 30fb11d..77ea6d9 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,7 +1,11 @@
 Gemfile.lock
 
+vendor/
+.bundle/
+
 _site/
 .sass-cache/
+.jekyll-metadata
 
 # For Mac and images
 .DS_Store