Bumping gaia.json for 2 gaia-central revision(s)

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https://hg.mozilla.org/integration/gaia-central/rev/e76887bfdff5
Author: Timothy Guan-tin Chien <timdream@gmail.com>
Desc: Merge pull request #10783 from marcofreda527/bug-888841-gaia-px

Bug 888841 - To use the specific value from device makefile for GAIA_DEV_PIXELS_PER_PX. r=timdream

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https://hg.mozilla.org/integration/gaia-central/rev/6e560635df07
Author: Marco Chen <mchen@mozilla.com>
Desc: Bug 888841 - To use the specific value from device makefile for GAIA_DEV_PIXELS_PER_PX. r=timdream.