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

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https://hg.mozilla.org/integration/gaia-central/rev/d88bfc7003f1
Author: Zac <zcampbell@mozilla.com>
Desc: Merge pull request #15942 from bebef1987/bug_964736

Bug 964736 - Rename a11y lockscreen tests

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https://hg.mozilla.org/integration/gaia-central/rev/75b10d5e28dd
Author: Bebe <bebe@mozilla.ro>
Desc: Bug 964736 - Rename a11y lockscreen tests
Bumping manifests a=b2g-bump