Bumping gaia.json for 1 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/2a438b8977aa
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Bug 1042534 - Disable failing test, TEST-UNEXPECTED-FAIL | /builds/slave/test/gaia/apps/verticalhome/test/marionette/search_test.js | Vertical - Search General walkthrough
Bumping manifests a=b2g-bump