Fix deprecation warnings in migrations

db/migrate/040_create_oauth_tables.rb

@@ -9,7 +9,7 @@ class CreateOauthTables < ActiveRecord::Migration
       t.string :secret, :limit => 50
       t.integer :user_id
 
-      t.timestamps
+      t.timestamps :null => true
     end
     add_index :client_applications, :key, :unique => true
 
@@ -20,7 +20,7 @@ class CreateOauthTables < ActiveRecord::Migration
       t.string :token, :limit => 50
       t.string :secret, :limit => 50
       t.timestamp :authorized_at, :invalidated_at
-      t.timestamps
+      t.timestamps :null => true
     end
 
     add_index :oauth_tokens, :token, :unique => true
@@ -29,7 +29,7 @@ class CreateOauthTables < ActiveRecord::Migration
       t.string :nonce
       t.integer :timestamp
 
-      t.timestamps
+      t.timestamps :null => true
     end
     add_index :oauth_nonces, [:nonce, :timestamp], :unique => true
   end

db/migrate/044_create_user_roles.rb

@@ -8,7 +8,7 @@ class CreateUserRoles < ActiveRecord::Migration
       t.column :user_id, :bigint, :null => false
       t.column :role, :user_role_enum, :null => false
 
-      t.timestamps
+      t.timestamps :null => true
     end
 
     User.where(:administrator => true).each do |user|

db/migrate/045_create_user_blocks.rb

@@ -10,7 +10,7 @@ class CreateUserBlocks < ActiveRecord::Migration
       t.column :needs_view,   :boolean,  :null => false, :default => false
       t.column :revoker_id,   :bigint
 
-      t.timestamps
+      t.timestamps :null => true
     end
 
     add_foreign_key :user_blocks, :users, :name => "user_blocks_user_id_fkey"

db/migrate/20120318201948_create_redactions.rb

@@ -6,7 +6,7 @@ class CreateRedactions < ActiveRecord::Migration
       t.string :title
       t.text :description
 
-      t.timestamps
+      t.timestamps :null => true
     end
 
     [:nodes, :ways, :relations].each do |tbl|