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

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https://hg.mozilla.org/integration/gaia-central/rev/4374625d5097
Author: Jan Keromnes <janx@linux.com>
Desc: Merge pull request #16091 from jankeromnes/developerhud

Bug 968220 - Add a "Developer HUD" sub-menu in "Developer". r=vingtetun

Note that this also deletes the Grid overlay.

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https://hg.mozilla.org/integration/gaia-central/rev/7caaa1965467
Author: Jan Keromnes <janx@linux.com>
Desc: Bug 968220 - Add a "Developer HUD" sub-menu in "Developer". r=vingtetun
Bumping manifests a=b2g-bump