Revert "`remove_column` does not take a type argument. [ci skip]. Closes #12864"

As of Rails 4.0 `remove_column` is no longer an alias for `remove_columns`.
The type is actually valid and used when issuing a rollback (new `change` method).

This reverts commit 9c9d4948e428a226a19aa92c17fa6ac5833c2fb8.

1 files changed, 1 insertions, 1 deletions

diff --git a/guides/source/migrations.md b/guides/source/migrations.md
index 93c7314779..71a177bca7 100644
--- a/guides/source/migrations.md
+++ b/guides/source/migrations.md
@@ -179,7 +179,7 @@ generates
 ```ruby
 class RemovePartNumberFromProducts < ActiveRecord::Migration
   def change
-    remove_column :products, :part_number
+    remove_column :products, :part_number, :string
   end
 end
 ```