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

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https://hg.mozilla.org/integration/gaia-central/rev/a4307d62e663
Author: Fernando Rodríguez Sela <frsela@tid.es>
Desc: Merge pull request #20986 from frsela/STK/Bug1027521

Bug 1027521 - [Sora]Phone returns to wrong screen when trying to return to previous screen in STK menu, r=jaoo

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https://hg.mozilla.org/integration/gaia-central/rev/d7ceecdc6b5f
Author: Fernando Rodriguez Sela <frsela@tid.es>
Desc: Bug 1027521 - [Sora]Phone returns to wrong screen when trying to return to previous screen in STK menu

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https://hg.mozilla.org/integration/gaia-central/rev/f704190fcfde
Author: Timothy Guan-tin Chien <timdream@gmail.com>
Desc: Merge pull request #21334 from timdream/keyboard-altmenu-ignore-multitouch

Bug 1033919 - Ignore multi-touch when alt char menu is shown, r=rudyl

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https://hg.mozilla.org/integration/gaia-central/rev/851f799af164
Author: Timothy Guan-tin Chien <timdream@gmail.com>
Desc: Bug 1033919 - Ignore multi-touch when alt char menu is shown
Bumping manifests a=b2g-bump