fix migration

db/migrate/20151208110020_add_note_to_users.rb

 class AddNoteToUsers < ActiveRecord::Migration
-  def change
-    add_column :users, :note, :text
+  def up
+    # Column "note" has been added to schema mistakenly (without actual migration),
+    # and this is why it can exist in some instances.
+    unless column_exists?(:users, :note)
+      add_column :users, :note, :text
+    end
+  end
+
+  def down
   end
 end