Fix custom_shaders example to avoid using 'output' variable name
Fix custom_shaders example to avoid using 'output' variable name

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