Make the destination folders

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

build-agda-html.rb

@@ -1,6 +1,7 @@
 require "json"
 require "set"
 require "optparse"
+require "fileutils"
 
 # For target_dir, use absolute paths because when invoking Agda, we'll be
 # using chdir.
@@ -56,6 +57,8 @@ files_for_paths.each do |path, files|
   Dir.chdir(original_wd)
   Dir.chdir(File.join(root_path, path))
   html_dir = File.join [target_dir, path, "html"]
+  FileUtils.mkdir_p html_dir
+
   files.each do |file|
     command = "#{ARGV[0]} --local-interfaces #{file} --html --html-dir=#{html_dir}"
     puts command