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

========

https://hg.mozilla.org/integration/gaia-central/rev/268588b14708
Author: Wilson Page <wilsonpage@me.com>
Desc: Merge pull request #26719 from wilsonpage/1081037

Update gaia-header to v0.5.4

========

https://hg.mozilla.org/integration/gaia-central/rev/88cff88f19d2
Author: Wilson Page <wilsonpage@me.com>
Desc: Update gaia-header to v0.5.4
Bumping manifests a=b2g-bump