Fix `mruby --verbose` (regression by #4827)

#### Before this patch:

  ```
  $ bin/mruby --verbose -e 'p 1'
  bin/mruby: Cannot open program file: --verbose
  ```

#### After this patch:

  ```
  $ bin/mruby --verbose -e 'p 1'
  00001 NODE_SCOPE:
  (snip)
  irep 0x7fe97041df30 nregs=4 nlocals=1 pools=0 syms=1 reps=0 iseq=11
  file: -e
      1 000 OP_LOADSELF R1
  (snip)

  1
  ```

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 b234b6c6f..f63ac9a30 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 --verbose option') do
+  assert_mruby(/\A[^\n]*NODE.*\n:end\n\z/m, "", true, %w[--verbose -e p(:end)])
+end
+
 assert('mruby --') do
   assert_mruby(%{["-x", "1"]\n}, "", true, %w[-e p(ARGV) -- -x 1])
 end