Bumping gaia.json for 4 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/b2b3191dbb2f
Author: Ryan VanderMeulen <rvandermeulen@mozilla.com>
Desc: Merge pull request #18716 from TheoChevalier/typography-fix

Bug 1001972 - [l10n][en-US] Typography consistency for 2.0

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https://hg.mozilla.org/integration/gaia-central/rev/bd7dc4435c80
Author: TheoChevalier <theo.chevalier11@gmail.com>
Desc: Bug 1001972 - [l10n][en-US] Typography consistency for 2.0

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https://hg.mozilla.org/integration/gaia-central/rev/f66ab36b2649
Author: Ryan VanderMeulen <rvandermeulen@mozilla.com>
Desc: Merge pull request #18677 from arky/General_L10N

Bug 1000859 - Add Xhosa xh locale

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https://hg.mozilla.org/integration/gaia-central/rev/16e2428b3376
Author: Arky <hitmanarky@gmail.com>
Desc: Bug 1000859 - Add Xhosa xh locale
Bumping manifests a=b2g-bump