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

========

https://hg.mozilla.org/integration/gaia-central/rev/4c54d883e936
Author: Douglas Sherk <github@sherk.me>
Desc: Merge pull request #17956 from DouglasSherk/965854-voicemail-sim-indicator

Bug 965854 - [DSDS][System] Display SIM indication in voicemail notification. r=etienne

========

https://hg.mozilla.org/integration/gaia-central/rev/0c000e9e4fce
Author: DouglasSherk <github@sherk.me>
Desc: Bug 965854 - [DSDS][System] Display SIM indication in voicemail notification. r=etienne
Bumping manifests a=b2g-bump