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

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https://hg.mozilla.org/integration/gaia-central/rev/39cf4deb11ae
Author: Jose M. Cantera <jmcanterafonseca@gmail.com>
Desc: Merge pull request #13569 from gtorodelvalle/contacts-bug-935307-user-details-via-settings

Bug 935307 - [B2G][Contacts] A user is able to retrieve a contact information from Settings screen

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https://hg.mozilla.org/integration/gaia-central/rev/7b92d2475afe
Author: Germán Toro del Valle <gtorodelvalle@gmail.com>
Desc: Bug 935307 - [B2G][Contacts] A user is able to retrieve a contact information from Settings screen

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https://hg.mozilla.org/integration/gaia-central/rev/0695adaab325
Author: Jose M. Cantera <jmcanterafonseca@gmail.com>
Desc: Merge pull request #13650 from rnowm/938028

Bug 938028 - Avoid CSS Gecko warnings and declaration drops due to unsupported font sizes

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https://hg.mozilla.org/integration/gaia-central/rev/14437edbed94
Author: rnowm <arnau@arnaumarch.com>
Desc: Bug 938028 - Avoid CSS Gecko warnings and declaration drops due to unsupported font sizes
Bug 937688 - Some small cosmetic changes to existing code. r=botond
Bug 937688 - Add a helper to APZCCallbackHelper to obtain the presShellId and viewId. r=botond
Bug 937688 - Refactor some code to extract a TabChild::GetDocument method. r=botond
Bug 937688 - Pass the presShellId and viewId from TabChild to RenderFrameParent when updating zoom constraints. r=botond
Bug 937688 - Pass the presShellId and viewId from TabChild to RenderFrameParent when requesting a zoom. r=botond
Bug 937688 - Make APZCTM::UpdateCompositionBounds explicitly operate on the root APZC for a layer tree. r=botond
Bug 937688 - Move ScrollableLayerGuid from APZCTreeManager.h to FrameMetrics.h. r=botond
Bug 937688 - Get the guid from ReceiveInputEvent and use it in the callback to ContentReceivedTouch. r=botond
Bug 937843 - Make some constructor arguments const. r=BenWa
Bug 937843 - Make an argument to nsLayoutUtils::FindIDFor const. r=tn
Bug 937843 - Make some things in APZCCallbackHelper const. r=botond