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

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https://hg.mozilla.org/integration/gaia-central/rev/181049c75f53
Author: vingtetun <21@vingtetun.org>
Desc: Merge pull request #17223 from vingtetun/bug984151

Bug 984151 - Make the contacts image pull up effect smoother. r=arcturus

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https://hg.mozilla.org/integration/gaia-central/rev/752987e94d55
Author: Vivien Nicolas <21@vingtetun.org>
Desc: Bug 984151 - Make the contacts image pull up effect smoother. r=arcturus

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https://hg.mozilla.org/integration/gaia-central/rev/de18d91d9202
Author: vingtetun <21@vingtetun.org>
Desc: Merge pull request #17337 from vingtetun/bug981610.shared

Bug 981610 - Remove some CSS warnings on shared/. r=arnau

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https://hg.mozilla.org/integration/gaia-central/rev/3e386227223e
Author: Vivien Nicolas <21@vingtetun.org>
Desc: Bug 981610 - Remove some CSS warnings on shared/. r=arnau
Bumping manifests a=b2g-bump