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

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https://hg.mozilla.org/integration/gaia-central/rev/bf639f09c3f0
Author: Fernando Campo <fernando.campo@o2.com>
Desc: Merge pull request #12936 from gitmai/bug-928283-back-sim-pin

Bug 928283- Added button back (r=fcampo)

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https://hg.mozilla.org/integration/gaia-central/rev/bd7ae70a5cce
Author: mai <mri@tid.es>
Desc: Bug 928283- Added button back