Bumping gaia.json for 7 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/3c886308136e
Author: Eitan Isaacson <eitan@monotonous.org>
Desc: Merge pull request #15568 from eeejay/bug-962318

Bug 962318 - Hide app iframe from accessibility when modal dialog is dis... r=alive

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https://hg.mozilla.org/integration/gaia-central/rev/082fae43308d
Author: Eitan Isaacson <eitan@monotonous.org>
Desc: Bug 962318 - Hide app iframe from accessibility when modal dialog is displayed.

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https://hg.mozilla.org/integration/gaia-central/rev/78e1c59f3b66
Author: Eitan Isaacson <eitan@monotonous.org>
Desc: Merge pull request #15211 from eeejay/bug-958649

Bug 958649 - Introduce accessibility UI tests. r=zac

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https://hg.mozilla.org/integration/gaia-central/rev/837a82502ffa
Author: Eitan Isaacson <eitan@monotonous.org>
Desc: Bug 958649 - Introduce lockscreen accessibility tests.

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https://hg.mozilla.org/integration/gaia-central/rev/0af7a71aaf93
Author: Eitan Isaacson <eitan@monotonous.org>
Desc: Bug 958649 - Introduce basic accessibility functionality for Gaia UI tests.

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https://hg.mozilla.org/integration/gaia-central/rev/fa63e31b5a76
Author: Eitan Isaacson <eitan@monotonous.org>
Desc: Merge pull request #15573 from eeejay/bug-962273

Bug 962273 - Update browser helper to use promise apps API. r=fabrice

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https://hg.mozilla.org/integration/gaia-central/rev/7023cbaebe8c
Author: Eitan Isaacson <eitan@monotonous.org>
Desc: Bug 962273 - Update browser helper to use promise apps API.
Bumping manifests a=b2g-bump