Update Gemfile

revert previous…erm…revert

Author: petecooper

Gemfile

@@ -4,7 +4,7 @@ gem "jekyll", "4.2.1"
 
 group :jekyll_plugins do
   gem "jekyll-feed", "0.16.0"
-  gem "jekyll-pwa-plugin", "2.2.3"
+  gem "jekyll-pwa-plugin", "5.1.5"
   gem "jekyll-seo-tag", "2.7.1"
   gem "jekyll-sitemap", "1.4.0"
 end