Fixed 1-7bit png writing.
Fixed 1-7bit png writing.

sumedhghaisas/node-dv,sumedhghaisas/node-dv,LoganArnett/node-dv,sumedhghaisas/node-dv,sumedhghaisas/node-dv,LoganArnett/node-dv,LoganArnett/node-dv,LoganArnett/node-dv