Fix Python detection for Python 3.x
Fix Python detection for Python 3.x

  File "<string>", line 1
    import sys; print sys.version_info[:2]
                        ^
SyntaxError: invalid syntax

jamesmarva/jsonschema,sightmachine/jsonschema,Julian/jsonschema,mathewmarcus/jsonschema,eodolphi/jsonschema,varunarya10/jsonschema,eodolphi/jsonschema,Julian/jsonschema,dnephin/jsonschema,python-jsonschema/jsonschema