Fix failing specs caused by $SAFE incompatibility on MRI 2.3
Fix failing specs caused by $SAFE incompatibility on MRI 2.3

    ArgumentError:
      $SAFE=2 to 4 are obsolete

rspec/rspec-core,azbshiri/rspec-core,xmik/rspec-core,azbshiri/rspec-core,rspec/rspec-core,xmik/rspec-core,rspec/rspec-core,xmik/rspec-core,azbshiri/rspec-core