Fix the version of imagemin-pngquant (#4915)
Fix the version of imagemin-pngquant (#4915)

Signed-off-by: Shaun Bent <434c135ae7b794a9e3518b87249d96c73cbafd5d@me.com>
0x80/gatsby,gatsbyjs/gatsby,gatsbyjs/gatsby,mingaldrichgan/gatsby,mingaldrichgan/gatsby,0x80/gatsby,gatsbyjs/gatsby,gatsbyjs/gatsby,fk/gatsby,fk/gatsby,ChristopherBiscardi/gatsby,gatsbyjs/gatsby,ChristopherBiscardi/gatsby,ChristopherBiscardi/gatsby,0x80/gatsby,ChristopherBiscardi/gatsby,fk/gatsby,gatsbyjs/gatsby,mingaldrichgan/gatsby