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

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https://hg.mozilla.org/integration/gaia-central/rev/74bdf9a0c027
Author: Timothy Guan-tin Chien <timdream@gmail.com>
Desc: Merge pull request #18466 from TheoChevalier/998449

Bug 998449 - Fix string reuse in "Cancel Install", r=timdream

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https://hg.mozilla.org/integration/gaia-central/rev/ca307198101b
Author: TheoChevalier <theo.chevalier11@gmail.com>
Desc: [Bug 998449] [B2G][l10n][Marketplace] "Cancel Install" string is used in both button and title
Bumping manifests a=b2g-bump