Ignore any argument in kernel exit proc

Otherwise a DOM Event object could be passed to Kernel#exit.

Author: elia

lib-opal/opal/rspec/browser.rb

@@ -5,7 +5,7 @@
 end
 
 # Trigger #at_exit callbacks once the DOM is ready
-kernel_exit = Kernel.method(:exit).to_proc
+kernel_exit = -> _ { Kernel.exit }
 if JS[:document].JS[:readyState] == :complete
   JS[:setTimeOut].call(kernel_exit, 1)
 else