Try use KaTeX for builds without NPM

blog/builder.sh

@@ -1,8 +1,5 @@
 source $stdenv/setup
 
-# Install KaTeX for back-end rendering.
-HOME="." npm install katex
-
 # Build site with Hugo
 cp -r $src/* .
 hugo --baseUrl="http://localhost:5000"

blog/default.nix

@@ -1,4 +1,4 @@
-{ stdenv, hugo, fetchgit, nodejs, ruby }:
+{ stdenv, hugo, fetchgit, katex, ruby }:
 
 let
     url = "https://dev.danilafe.com/Web-Projects/blog-static.git";
@@ -13,5 +13,5 @@ in
         };
         builder = ./builder.sh;
         converter = ./convert.rb;
-        buildInputs = [ hugo nodejs (ruby.withPackages (ps: [ ps.nokogiri ])) ];
+        buildInputs = [ hugo katex (ruby.withPackages (ps: [ ps.nokogiri ])) ];
     }