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

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https://hg.mozilla.org/integration/gaia-central/rev/a76939959165
Author: John Hu <johu@mozilla.com>
Desc: Merge pull request #12763 from punamdahiya/Bug920387_Wallpaper_Share_Activity

Bug920387 - [Gallery] - Update Wallpaper share activity to use blob instead of data URL r=davidflanagan

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https://hg.mozilla.org/integration/gaia-central/rev/4eedc0f6d80d
Author: Punam Dahiya <punamdahiya@yahoo.com>
Desc: Bug920387 - [Gallery] - Update Wallpaper share activity to use blob instead of data URL r=davidflanagan