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

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https://hg.mozilla.org/integration/gaia-central/rev/1bf9ece3c16f
Author: gasolin <gasolin@gmail.com>
Desc: Merge pull request #16976 from gasolin/issue-980775

Bug 980775 - [Resource] rename incorrect 1.5.png to 1.5x.png, r=pivanov

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https://hg.mozilla.org/integration/gaia-central/rev/6d219cf2cf28
Author: gasolin <gasolin@gmail.com>
Desc: Bug 980775 - [Resource] rename incorrect 1.5.png to 1.5x.png
Bumping manifests a=b2g-bump