mruby-io: standardize block parameter spacing

changed block spacing from { | to {| for consistency.

Co-authored-by: Claude <noreply@anthropic.com>

mrbgems/mruby-io/mrblib/kernel.rb

@@ -11,7 +11,7 @@ module Kernel
   #   `echo oops && exit 99`   #=> "oops\n"
   #
   private def `(cmd) #`
-    IO.popen(cmd) { |io| io.read }
+    IO.popen(cmd) {|io| io.read }
   end
 
   #