Bumping gaia.json for 4 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-2_0/rev/4a8266924fe8
Author: Jose M. Cantera <jmcanterafonseca@gmail.com>
Desc: Merge pull request #22033 from jmcanterafonseca/fix_loop_at_last

Bug 1017756 - Update Loop buttons & state (color, name, visibility...) i...

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https://hg.mozilla.org/integration/gaia-2_0/rev/08f66b9b5028
Author: punamdahiya <punamdahiya@yahoo.com>
Desc: Merge pull request #21985 from punamdahiya/Bug1035492-Wallpaper

Bug1035492-[Wallpaper]-Use Img element instead of background images for gecko to handle decoded image memory r=djf

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https://hg.mozilla.org/integration/gaia-2_0/rev/a4895b615dcf
Author: Ryan VanderMeulen <rvandermeulen@mozilla.com>
Desc: Merge pull request #22050 from justindarc/bug1037880-v2.0

Bug 1037880 - FM radio should stop sound in speaker mode when I receive ...

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https://hg.mozilla.org/integration/gaia-2_0/rev/029062ff5ae4
Author: Justin D'Arcangelo <justindarc@gmail.com>
Desc: Bug 1037880 - FM radio should stop sound in speaker mode when I receive an incoming call
Bumping manifests a=b2g-bump