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

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https://hg.mozilla.org/integration/gaia-central/rev/df47d1701c1a
Author: George <georgeiscoming@gmail.com>
Desc: Merge pull request #23943 from cctuan/1062730

Bug 1062730 - [NFC] Home button could not work well after receiving multiple websites which are shared via NFC

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https://hg.mozilla.org/integration/gaia-central/rev/6de441d8c713
Author: cctuan <georgeiscoming@gmail.com>
Desc:  Bug 1062730 - [NFC] Home button could not work well after receiving multiple websites which are shared via NFC
1. publish activeappchanged when app is changed in app_window_manager.js
2. stop tiltiing effect if receiving activeappchanged event

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https://hg.mozilla.org/integration/gaia-central/rev/33d147229413
Author: George <georgeiscoming@gmail.com>
Desc: Merge pull request #24198 from cctuan/1065943

Bug 1065943 - [Text Selection] Hide utility bubble when scrolling and show bubble when scroll end

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https://hg.mozilla.org/integration/gaia-central/rev/8582124fef8f
Author: cctuan <georgeiscoming@gmail.com>
Desc: Bug 1065943 - [Text Selection] Hide utility bubble when scrolling and show bubble when scroll end - gaia part
Bumping manifests a=b2g-bump