Adjust build script to accept Agda invocation

This might come in useful from NixOS

Signed-off-by: Danila Fedorin <danila.fedorin@gmail.com>

build-agda-html.rb

@@ -31,6 +31,6 @@ files_for_paths.each do |path, files|
   Dir.chdir(File.join [original_wd, path])
   files.each do |file|
     puts "Invoking 'agda' on file: #{File.join [Dir.getwd, file]}"
-    `agda --local-interfaces #{file} --html --html-dir=html`
+    `#{ARGV[0]} --local-interfaces #{file} --html --html-dir=html`
   end
 end