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

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https://hg.mozilla.org/integration/gaia-central/rev/14f4dab239d1
Author: Zac <zcampbell@mozilla.com>
Desc: Bug 1084426 - Add default external tags to manifest files a=test-only r=me
Bumping manifests a=b2g-bump