Locales: Update Asturian locale definition

[ocean90]

Original request: https://make.wordpress.org/polyglots/2016/02/04/hi-polyglots-my-name-is-chris-miller-and

Ethnologue reference: http://www.ethnologue.com/language/ast

Data:

$ast = new GP_Locale();
$ast->english_name = 'Asturian';
$ast->native_name = 'Asturianu';
$ast->lang_code_iso_639_2 = 'ast';
$ast->lang_code_iso_639_3 = 'ast';
$ast->country_code = 'es';
$ast->wp_locale = 'ast';
$ast->slug = 'ast';