mruby-set/mrbgem.rake: add test dependency.
The `instance_variable_get` has been separated to `mruby-metaprog` gem,
so we need to specify the gem as test dependency.
@@ -4,4 +4,5 @@ MRuby::Gem::Specification.new('mruby-set') do |spec|
spec.add_dependency "mruby-hash-ext", :core => "mruby-hash-ext"
spec.add_dependency "mruby-enumerator", :core => "mruby-enumerator"
+ spec.add_test_dependency "mruby-metaprog", :core => "mruby-metaprog"
end
