Avoid uses mruby/src/error.h file

mrbgems/mruby-dir/mrbgem.rake

@@ -1,6 +1,4 @@
 MRuby::Gem::Specification.new('mruby-dir') do |spec|
   spec.license = 'MIT and MIT-like license'
   spec.authors = [ 'Internet Initiative Japan Inc.', 'Kevlin Henney']
-
-  spec.cc.include_paths << "#{build.root}/src"
 end

mrbgems/mruby-dir/src/dir.c

@@ -7,8 +7,8 @@
 #include "mruby.h"
 #include "mruby/class.h"
 #include "mruby/data.h"
+#include "mruby/error.h"
 #include "mruby/string.h"
-#include "error.h"
 #include <sys/types.h>
 #if defined(_WIN32) || defined(_WIN64)
   #define MAXPATHLEN 1024