Fix linting errors in locale/index.js

.eslintignore

@@ -8,4 +8,4 @@
 karma.config.js
 webpack.config.js
 svg.config.js
-/app/assets/javascripts/locale/**/*.js
+/app/assets/javascripts/locale/**/app.js

app/assets/javascripts/locale/index.js

@@ -16,9 +16,8 @@ const locales = allLocales.reduce((d, obj) => {
   return data;
 }, {});
 
-let lang = document.querySelector('html').getAttribute('lang') || 'en';
-lang = lang.replace(/-/g, '_');
-
+const langAttribute = document.querySelector('html').getAttribute('lang');
+const lang = (langAttribute || 'en').replace(/-/g, '_');
 const locale = new Jed(locales[lang]);
 
 /**