Use mail_tel parameter for logging in

http://blog.nicovideo.jp/niconews/ni051130.html

They now have new login page.

They have kept old parameter name work, but following the present state
for future change.

lib/niconico.rb

@@ -79,7 +79,7 @@ class LoginError < StandardError; end
   private
 
   def login_with_email
-    page = @agent.post(URL[:login], 'mail' => @mail, 'password' => @pass)
+    page = @agent.post(URL[:login], 'mail_tel' => @mail, 'password' => @pass)
 
     raise LoginError, "Failed to log in (x-niconico-authflag is 0)" if page.header["x-niconico-authflag"] == '0'
     @token = nil