Apply :core parameter to default.gembox

mrbgems/default.gembox

 MRuby::GemBox.new do |conf|
   # Use standard Kernel#sprintf method
-  conf.gem "#{root}/mrbgems/mruby-sprintf"
+  conf.gem :core => "mruby-sprintf"
 
   # Use standard print/puts/p
-  conf.gem "#{root}/mrbgems/mruby-print"
+  conf.gem :core => "mruby-print"
 
   # Use standard Math module
-  conf.gem "#{root}/mrbgems/mruby-math"
+  conf.gem :core => "mruby-math"
 
   # Use standard Time class
-  conf.gem "#{root}/mrbgems/mruby-time"
+  conf.gem :core => "mruby-time"
 
   # Use standard Struct class
-  conf.gem "#{root}/mrbgems/mruby-struct"
+  conf.gem :core => "mruby-struct"
 
   # Use extensional Enumerable module
-  conf.gem "#{root}/mrbgems/mruby-enum-ext"
+  conf.gem :core => "mruby-enum-ext"
 
   # Use extensional String class
-  conf.gem "#{root}/mrbgems/mruby-string-ext"
+  conf.gem :core => "mruby-string-ext"
 
   # Use extensional Numeric class
-  conf.gem "#{root}/mrbgems/mruby-numeric-ext"
+  conf.gem :core => "mruby-numeric-ext"
 
   # Use extensional Array class
-  conf.gem "#{root}/mrbgems/mruby-array-ext"
+  conf.gem :core => "mruby-array-ext"
 
   # Use extensional Hash class
-  conf.gem "#{root}/mrbgems/mruby-hash-ext"
+  conf.gem :core => "mruby-hash-ext"
 
   # Use extensional Range class
-  conf.gem "#{root}/mrbgems/mruby-range-ext"
+  conf.gem :core => "mruby-range-ext"
 
   # Use extensional Proc class
-  conf.gem "#{root}/mrbgems/mruby-proc-ext"
+  conf.gem :core => "mruby-proc-ext"
 
   # Use extensional Symbol class
-  conf.gem "#{root}/mrbgems/mruby-symbol-ext"
+  conf.gem :core => "mruby-symbol-ext"
 
   # Use Random class
-  conf.gem "#{root}/mrbgems/mruby-random"
+  conf.gem :core => "mruby-random"
 
   # Generate mirb command
-  conf.gem "#{root}/mrbgems/mruby-bin-mirb"
+  conf.gem :core => "mruby-bin-mirb"
 
   # Generate mruby command
-  conf.gem "#{root}/mrbgems/mruby-bin-mruby"
+  conf.gem :core => "mruby-bin-mruby"
 end