bundler: fix bundle version git error

It seems that `bundle version` calls git to know the commit sha, while `bundle --version` only shows the version of bundler.

Fixes #6988

plugins/bundler/bundler.plugin.zsh

@@ -55,7 +55,7 @@ done
 
 bundle_install() {
   if _bundler-installed && _within-bundled-project; then
-    local bundler_version=`bundle version | cut -d' ' -f3`
+    local bundler_version=`bundle --version | cut -d' ' -f3`
     if [[ $bundler_version > '1.4.0' || $bundler_version = '1.4.0' ]]; then
       if [[ "$OSTYPE" = (darwin|freebsd)* ]]
       then