Support `--` (end of options) to `mruby` command

#### Before this patch:

  ```
  $ bin/mruby -e 'p ARGV' -- -x
  bin/mruby: invalid option -- (-h will show valid options)
  ```

#### After this patch:

  ```
  $ bin/mruby -e 'p ARGV' -- -x
  ["-x"]
  ```

1 files changed, 4 insertions, 0 deletions

diff --git a/mrbgems/mruby-bin-mruby/bintest/mruby.rb b/mrbgems/mruby-bin-mruby/bintest/mruby.rb
index df0e991f7..b234b6c6f 100644
--- a/mrbgems/mruby-bin-mruby/bintest/mruby.rb
+++ b/mrbgems/mruby-bin-mruby/bintest/mruby.rb
@@ -128,6 +128,10 @@ assert('mruby -r option (file not found)') do
   assert_mruby("", /\A.*: Cannot open library file: .*\n\z/, false, %w[-r _no_exists_])
 end
 
+assert('mruby --') do
+  assert_mruby(%{["-x", "1"]\n}, "", true, %w[-e p(ARGV) -- -x 1])
+end
+
 assert('mruby invalid short option') do
   assert_mruby("", /\A.*: invalid option -1 .*\n\z/, false, %w[-1])
 end