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

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https://hg.mozilla.org/integration/gaia-central/rev/fed38c23695e
Author: Zac Campbell <zcampbell@mozilla.com>
Desc: Bug 973232 - Address TBPL failure in test_settings_wallpaper with larger timeout r=me a=testonly
Bumping manifests a=b2g-bump