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

========

https://hg.mozilla.org/integration/gaia-central/rev/6b4220465f38
Author: steveck-chung <schung@mozilla.com>
Desc: Merge pull request #16951 from steveck-chung/Bug-976999

Bug 976999 - [Sora][Message][MMS]Some of the text content lost when forward the MMS. r=julienw

========

https://hg.mozilla.org/integration/gaia-central/rev/054964ce6a67
Author: Steve Chung <schung@mozilla.com>
Desc: Bug 976999 - [Sora][Message][MMS]Some of the text content lost when forward the MMS
Bumping manifests a=b2g-bump