Fix ipynb for py3k
Fix ipynb for py3k

The lines for checksum I took from pypng. Not 100% sure though
because the pyvnc does not work for me (neither py3k and py 2.x).
At least no more errors on python3.

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