Load from root bundler when running from git

middleman-core/lib/middleman-core/core_extensions/extensions.rb

@@ -137,7 +137,10 @@ module Middleman
             instance_eval File.read(local_config), local_config, 1
           end
           
-          activate(:sprockets) if autoload_sprockets
+          if autoload_sprockets
+            require "middleman-sprockets"
+            activate(:sprockets)
+          end
       
           run_hook :build_config if build?
           run_hook :development_config if development?