Fix class name validation in `Struct.new`

Before this patch:

  $ bin/mruby -e 'p Struct.new("A-")'
  #=> Struct::"A-"

After this patch:

  $ bin/mruby -e 'p Struct.new("A-")'
  #=> NameError: identifier A- needs to be constant

1 files changed, 4 insertions, 0 deletions

diff --git a/mrbgems/mruby-struct/test/struct.rb b/mrbgems/mruby-struct/test/struct.rb
index 91e8cecc6..9f2ff1cdc 100644
--- a/mrbgems/mruby-struct/test/struct.rb
+++ b/mrbgems/mruby-struct/test/struct.rb
@@ -181,6 +181,10 @@ assert("Struct.new does not allow array") do
   end
 end
 
+assert("Struct.new does not allow invalid class name") do
+  assert_raise(NameError) { Struct.new("Test-", :a) }
+end
+
 assert("Struct.new generates subclass of Struct") do
   begin
     original_struct = Struct