Update Python 3 PyPI classifiers.
Update Python 3 PyPI classifiers.

Python 3.*3*+ is currently supported.

kkuunnddaannkk/vispy,Eric89GXL/vispy,ghisvail/vispy,jay3sh/vispy,bollu/vispy,hronoses/vispy,jay3sh/vispy,QuLogic/vispy,jay3sh/vispy,dchilds7/Deysha-Star-Formation,sh4wn/vispy,drufat/vispy,dchilds7/Deysha-Star-Formation,jdreaver/vispy,michaelaye/vispy,sbtlaarzc/vispy,julienr/vispy,hronoses/vispy,hronoses/vispy,sbtlaarzc/vispy,RebeccaWPerry/vispy,kkuunnddaannkk/vispy,jdreaver/vispy,RebeccaWPerry/vispy,QuLogic/vispy,bollu/vispy,Eric89GXL/vispy,jdreaver/vispy,sbtlaarzc/vispy,julienr/vispy,srinathv/vispy,Eric89GXL/vispy,QuLogic/vispy,drufat/vispy,inclement/vispy,RebeccaWPerry/vispy,julienr/vispy,inclement/vispy,drufat/vispy,srinathv/vispy,ghisvail/vispy,ghisvail/vispy,sh4wn/vispy,inclement/vispy,kkuunnddaannkk/vispy,michaelaye/vispy,sh4wn/vispy,michaelaye/vispy,srinathv/vispy,bollu/vispy,dchilds7/Deysha-Star-Formation