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

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https://hg.mozilla.org/integration/gaia-central/rev/f1fb72bb2f17
Author: Fernando Jiménez Moreno <ferjmoreno@gmail.com>
Desc: Merge pull request #15293 from borjasalguero/fix_intro_html_fxa

Bug 959509 - fxa/elements/fxa-intro.html could not be found r=ferjm

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https://hg.mozilla.org/integration/gaia-central/rev/6629ec6a291d
Author: borjasalguero <fbsc@tid.es>
Desc: Bug 959509 - fxa/elements/fxa-intro.html could not be found r=ferjm