Add API hook for modifying upserted pages (#863)
Add API hook for modifying upserted pages (#863)


fk/gatsby,mickeyreiss/gatsby,gatsbyjs/gatsby,danielfarrell/gatsby,danielfarrell/gatsby,okcoker/gatsby,gatsbyjs/gatsby,okcoker/gatsby,fabrictech/gatsby,ChristopherBiscardi/gatsby,fabrictech/gatsby,okcoker/gatsby,ChristopherBiscardi/gatsby,fk/gatsby,mickeyreiss/gatsby,0x80/gatsby,danielfarrell/gatsby,0x80/gatsby,chiedo/gatsby,chiedo/gatsby,Khaledgarbaya/gatsby,ChristopherBiscardi/gatsby,gatsbyjs/gatsby,mingaldrichgan/gatsby,chiedo/gatsby,0x80/gatsby,Khaledgarbaya/gatsby,gatsbyjs/gatsby,fk/gatsby,gatsbyjs/gatsby,mickeyreiss/gatsby,ChristopherBiscardi/gatsby,mingaldrichgan/gatsby,mingaldrichgan/gatsby,Khaledgarbaya/gatsby,fabrictech/gatsby,gatsbyjs/gatsby