Bundle update

Gemfile.lock

 GIT
   remote: git://github.com/activeadmin/activeadmin.git
-  revision: c1817a1a2a1e658300b73e3838a520479d3c1a7a
+  revision: 169bad98f2746be19b71357bb16a81065640a337
   specs:
     activeadmin (1.0.0.pre4)
       arbre (~> 1.0, >= 1.0.2)
@@ -365,7 +365,7 @@ GEM
       simplecov-html (~> 0.10.0)
     simplecov-html (0.10.0)
     slop (3.6.0)
-    spring (2.0.0)
+    spring (2.0.1)
       activesupport (>= 4.2)
     sprockets (3.7.1)
       concurrent-ruby (~> 1.0)