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

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https://hg.mozilla.org/integration/gaia-1_3/rev/18107ca5f6a9
Author: Cristian Rodriguez <crdlc@tid.es>
Desc: Merge pull request #16693 from crdlc/bug-header-contacts-paint

Bug 972091 - [B2G][Contacts] Header bar, search bar and all contacts can be completely missing on the main contacts' view window

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https://hg.mozilla.org/integration/gaia-1_3/rev/ed292b10ccf1
Author: crdlc <crdlc@tid.es>
Desc: Bug 972091 - [B2G][Contacts] Header bar, search bar and all contacts can be completely missing on the main contacts view window
Bumping manifests a=b2g-bump
Bug 974643 - The displayport is not relevant to position: fixed content, only to scrolling content. r=roc, a=fabrice

The relevant part of postion: fixed items lies within the viewport, which is the scroll position clamping scroll port size if one has been set.
Merge b2g28 to v1.3t. a=merge