Add gemfiles with Nokogiri

Gemfile

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+source 'https://rubygems.org'
+
+gem 'nokogiri'

Gemfile.lock

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+GEM
+  remote: https://rubygems.org/
+  specs:
+    mini_portile2 (2.8.0)
+    nokogiri (1.13.3)
+      mini_portile2 (~> 2.8.0)
+      racc (~> 1.4)
+    racc (1.6.0)
+
+PLATFORMS
+  ruby
+
+DEPENDENCIES
+  nokogiri
+
+BUNDLED WITH
+   2.1.4

gemset.nix

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+{
+  mini_portile2 = {
+    groups = ["default"];
+    platforms = [];
+    source = {
+      remotes = ["https://rubygems.org"];
+      sha256 = "0rapl1sfmfi3bfr68da4ca16yhc0pp93vjwkj7y3rdqrzy3b41hy";
+      type = "gem";
+    };
+    version = "2.8.0";
+  };
+  nokogiri = {
+    dependencies = ["mini_portile2" "racc"];
+    groups = ["default"];
+    platforms = [];
+    source = {
+      remotes = ["https://rubygems.org"];
+      sha256 = "1p6b3q411h2mw4dsvhjrp1hh66hha5cm69fqg85vn2lizz71n6xz";
+      type = "gem";
+    };
+    version = "1.13.3";
+  };
+  racc = {
+    groups = ["default"];
+    platforms = [];
+    source = {
+      remotes = ["https://rubygems.org"];
+      sha256 = "0la56m0z26j3mfn1a9lf2l03qx1xifanndf9p3vx1azf6sqy7v9d";
+      type = "gem";
+    };
+    version = "1.6.0";
+  };
+}