Update nokogiri for security

Author: PeterJCLaw

Gemfile.lock

@@ -59,10 +59,10 @@ GEM
     neat (3.0.0)
       sass (~> 3.4)
       thor (~> 0.19)
-    nokogiri (1.15.5)
+    nokogiri (1.15.6)
       mini_portile2 (~> 2.8.2)
       racc (~> 1.4)
-    nokogiri (1.15.5-x64-mingw32)
+    nokogiri (1.15.6-x64-mingw32)
       racc (~> 1.4)
     parallel (1.22.1)
     pathutil (0.16.2)