activerecord-sqlserver-adapter nvarchar datatype length

I've recently installed this adapter in hope that I can work with
utf-8
encoding using the SQL Server nvarchar data type. I've installed and
followed the steps detailed at this uri:
http://github.com/adzap/rails-sqlserver-adapter/tree/master

I have this following migration class definition:
class CreateContacts < ActiveRecord::Migration
    def self.up
          create_table :contacts do |t|
            t.column :organization_id, :integer, :null=>false
            t.column :first_name, :nvarchar, :limit=>10, :null=>false
            t.column :last_name, :nvarchar, :null=>false
            t.column :title, :string
            t.column :contact_type_id, :integer, :null=>false
            t.column :fax, :string
            t.timestamps
        end
    end

    def self.down
        drop_table :contacts
    end
end

When I look at the generated table definition, the first_name column
created has a length of 2 rather than 10 as specified by the :limit
parameter.
In fact all of the columns of type :nvarchar get a length of 2. If I
try what the web site
documentation has, namely:

t.column :body2_utf8, :nvarchar_max # Creates nvarchar(max)
or in my case:
t.column :first_name, :nvarchar_max, :null=>false

I get an error that says:
DBI::DatabaseError: Execute
    OLE error code:80040E14 in Microsoft OLE DB Provider for SQL
Server
      Column, parameter, or variable #3: Cannot find data type
nvarchar_max.
    HRESULT error code:0x80020009

What is the correct way to set the maximum length of the nvarchar data
type?