hotfix index gsp pages in i18n (#131)

Author: lindsaylevine

lib/helpers/getPrerenderManifest.js

@@ -15,7 +15,8 @@ const transformManifestForI18n = (manifest) => {
         newRoutes[route] = routes[route];
       } else {
         locales.forEach((locale) => {
-          const routeWithPrependedLocale = `/${locale}${route}`;
+          const routeWithPrependedLocale =
+            route === "/" ? `/${locale}` : `/${locale}${route}`;
           newRoutes[routeWithPrependedLocale] = {
             dataRoute: getDataRouteForRoute(route, locale),
             srcRoute: route,