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

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https://hg.mozilla.org/integration/gaia-central/rev/be8d7643de18
Author: Jose M. Cantera <jmcanterafonseca@gmail.com>
Desc: Merge pull request #13917 from rnowm/FB-headers-refresh

Bug 941541 - Visual refreshment has caused regressions in import views

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https://hg.mozilla.org/integration/gaia-central/rev/8690ddcac165
Author: rnowm <arnau@arnaumarch.com>
Desc: Bug 941541 - Visual refreshment has caused regressions in import views