Merge pull request #4202 from shuujii/simplify-full-core-gembox

Simplify full-core.gembox

mrbgems/full-core.gembox

 MRuby::GemBox.new do |conf|
-  conf.gem :core => "mruby-sprintf"
-  conf.gem :core => "mruby-print"
-
   Dir.glob("#{root}/mrbgems/mruby-*/mrbgem.rake") do |x|
     g = File.basename File.dirname x
-    conf.gem :core => g unless g =~ /^mruby-(print|sprintf|bin-debugger|test)$/
+    conf.gem :core => g unless g =~ /^mruby-(?:bin-debugger|test)$/
   end
 end