bundler: support new file naming convention (#6594)

plugins/bundler/bundler.plugin.zsh

@@ -82,7 +82,7 @@ _bundler-installed() {
 _within-bundled-project() {
   local check_dir="$PWD"
   while [ "$check_dir" != "/" ]; do
-    [ -f "$check_dir/Gemfile" ] && return
+    [ -f "$check_dir/Gemfile" -o -f "$check_dir/gems.rb" ] && return
     check_dir="$(dirname $check_dir)"
   done
   false