[rubygems/rubygems] Prefer `install_path` alias

For consistency with the rest of usages in this class.

https://github.com/rubygems/rubygems/commit/69f9ab34b1

lib/bundler/source/git.rb

@@ -216,7 +216,7 @@ module Bundler
       def cache(spec, custom_path = nil)
         app_cache_path = app_cache_path(custom_path)
         return unless Bundler.feature_flag.cache_all?
-        return if path == app_cache_path
+        return if install_path == app_cache_path
         cached!
         FileUtils.rm_rf(app_cache_path)
         git_proxy.checkout if requires_checkout?