jekyll: add jekyll-polyglot

pkgs/applications/misc/jekyll/full/Gemfile

···
 gem "jekyll-feed", "~> 0.9"
 gem "jekyll-gist"
 gem "jekyll-paginate"
+gem "jekyll-polyglot"
 gem "jekyll-redirect-from"
 gem "kramdown-syntax-coderay"
 gem "mime-types", "~> 3.0"

pkgs/applications/misc/jekyll/full/Gemfile.lock

···
       html-pipeline (~> 2.3)
       jekyll (>= 3.7, < 5.0)
     jekyll-paginate (1.1.0)
+    jekyll-polyglot (1.3.3)
+      jekyll (>= 3.0)
     jekyll-redirect-from (0.16.0)
       jekyll (>= 3.3, < 5.0)
     jekyll-sass-converter (2.1.0)
···
   jekyll-gist
   jekyll-mentions
   jekyll-paginate
+  jekyll-polyglot
   jekyll-redirect-from
   jekyll-seo-tag
   jekyll-sitemap

pkgs/applications/misc/jekyll/full/gemset.nix

···
     };
     version = "1.1.0";
   };
+  jekyll-polyglot = {
+    dependencies = ["jekyll"];
+    groups = ["default"];
+    platforms = [];
+    source = {
+      remotes = ["https://rubygems.org"];
+      sha256 = "4ad9140733250b65bc1ffab84650c588d036d23129e82f0349d31e56f1fe10a8";
+      type = "gem";
+    };
+    version = "1.3.3";
+  };
   jekyll-redirect-from = {
     dependencies = ["jekyll"];
     groups = ["default"];
···
     };
     version = "2.4.2";
   };
-}
+}