Update rails_admin to version 0.6.4

Gemfile.lock

@@ -73,7 +73,7 @@ GEM
     jquery-rails (3.1.2)
       railties (>= 3.0, < 5.0)
       thor (>= 0.14, < 2.0)
-    jquery-ui-rails (4.2.1)
+    jquery-ui-rails (5.0.0)
       railties (>= 3.2.16)
     json (1.8.1)
     kaminari (0.16.1)
@@ -121,20 +121,20 @@ GEM
     rails_12factor (0.0.2)
       rails_serve_static_assets
       rails_stdout_logging
-    rails_admin (0.6.3)
+    rails_admin (0.6.4)
       builder (~> 3.1)
       coffee-rails (~> 4.0)
       font-awesome-rails (>= 3.0)
       haml (~> 4.0)
       jquery-rails (~> 3.0)
-      jquery-ui-rails (~> 4.0)
+      jquery-ui-rails (~> 5.0)
       kaminari (~> 0.14)
       nested_form (~> 0.3)
       rack-pjax (~> 0.7)
       rails (~> 4.0)
       remotipart (~> 1.0)
       safe_yaml (~> 1.0)
-      sass-rails (~> 4.0)
+      sass-rails (>= 4.0)
     rails_serve_static_assets (0.0.2)
     rails_stdout_logging (0.0.3)
     railties (4.1.6)