Bumping gaia.json for 2 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/6005edf7faa2
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Merge pull request #21834 from KevinGrandon/bug_1029902_low_memory_features

Bug 1029902 - [Vertical Homescreen] Implement device capability configuration

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https://hg.mozilla.org/integration/gaia-central/rev/7468f3ab39d5
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Bug 1040070 - [Verical Homescreen] Use smaller images sizes for low capability devices r=crdlc

The following changes are made for low capability devices:

* Icons default to 4 per row.
* Icon resolution is reduced.
* Icon rendering does not account for devicePixelRatio.
Bumping manifests a=b2g-bump