Use mruby-print only exist for latest master

Author: take-cheeze

mrbgem.rake

@@ -3,6 +3,6 @@ MRuby::Gem::Specification.new('mruby-stringio') do |spec|
   spec.author  = 'ksss <[email protected]>'
   spec.summary = 'StringIO class'
 
-  spec.add_dependency('mruby-print', core: 'mruby-print')
+  spec.add_dependency('mruby-print', core: 'mruby-print') if Dir.exist? "#{MRUBY_ROOT}/mrbgems/mruby-print"
   spec.add_dependency('mruby-enumerator', core: 'mruby-enumerator')
 end