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

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https://hg.mozilla.org/integration/gaia-1_4/rev/79f9cff940e6
Author: Marshall Culpepper <marshall.law@gmail.com>
Desc: Merge pull request #17857 from marshall/ftuPing_v1.4

Bug 969101: Initial implementation of a first-time use ping

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https://hg.mozilla.org/integration/gaia-1_4/rev/f91834b3b0b3
Author: Marshall Culpepper <marshall@mozilla.com>
Desc: Bug 969101: Initial implementation of a first-time use ping. r=fabrice a=1.4+, bajaj
Bumping manifests a=b2g-bump