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

========

https://hg.mozilla.org/integration/gaia-central/rev/5b4d3028e817
Author: dwi2 <dwi2@dwi2.com>
Desc: Merge pull request #15960 from dwi2/bug964755

Bug 964755 - Make sure WifiHelper.getCapabilities() return non-null valu...

========

https://hg.mozilla.org/integration/gaia-central/rev/5dbc35834894
Author: tzhuang <tzhuang@mozilla.com>
Desc: Bug 964755 - Make sure WifiHelper.getCapabilities() return non-null value for network not in the air
Bumping manifests a=b2g-bump