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

========

https://hg.mozilla.org/integration/gaia-central/rev/5dc28b6fc799
Author: Albert <acperez@tid.es>
Desc: Merge pull request #12676 from acperez/bug-923766

Bug 923766 - Single variant applications are not placed in correct position in the homescreen

========

https://hg.mozilla.org/integration/gaia-central/rev/8e9525869484
Author: Albert <acperez@tid.es>
Desc: Bug 923766 - Single variant applications are not placed in correct position in the homescreen