auto download CJK fonts

Author: Sherry520

Rakefile

@@ -1,5 +1,15 @@
+def exec_or_raise(command)
+  puts `#{command}`
+  if (! $?.success?)
+    raise "'#{command}' failed"
+  end
+end
+
 namespace :book do
 
+  # Download asciidoctor-pdf-cjk-kai_gen_gothic
+  exec_or_raise("asciidoctor-pdf-cjk-kai_gen_gothic-install")
+
   # Variables referenced for build
   version_string = `git describe --tags --abbrev=0`.chomp
   if version_string.empty?