Simplify & fix vendorized six import in pexpect
Simplify & fix vendorized six import in pexpect

mattrobenolt/invoke,mattrobenolt/invoke,pyinvoke/invoke,singingwolfboy/invoke,frol/invoke,pfmoore/invoke,mkusz/invoke,pyinvoke/invoke,kejbaly2/invoke,sophacles/invoke,mkusz/invoke,tyewang/invoke,frol/invoke,kejbaly2/invoke,pfmoore/invoke