[orange] Fix StringIO import to be compatible with python3
Orange module imports StringIO from StringIO. This does not work with python 3 anymore. To fix this, and still be compatible with python 2.7, StringIO should be imported from io.
Orange module imports StringIO from StringIO. This does not work with python 3 anymore. To fix this, and still be compatible with python 2.7, StringIO should be imported from io.