Specify lang option for gatsby-plugin-manifest

Author: lex111

gatsby-config.js

@@ -163,7 +163,9 @@ module.exports = {
       resolve: `gatsby-plugin-manifest`,
       options: {
         name: 'React Docs',
-        short_name: 'React',
+        short_name: 'React', // eg. React [%LANG_CODE%]
+        // Translators: please change this and two above options (see https://www.gatsbyjs.org/packages/gatsby-plugin-manifest/#feature-configuration---optional)
+        lang: 'en',
         start_url: '/',
         background_color: '#20232a',
         theme_color: '#20232a',