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

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https://hg.mozilla.org/integration/gaia-1_4/rev/b06b8a9e34f4
Author: Timothy Guan-tin Chien <timdream@gmail.com>
Desc: Merge pull request #18966 from timdream/two-homescreen

Bug 996514 - Don't homescreenWindow.render() twice, r=alive
Conflicts:
	apps/system/js/app_window.js

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https://hg.mozilla.org/integration/gaia-1_4/rev/f1f36a922897
Author: Jan Jongboom <janjongboom@gmail.com>
Desc: Bug 992346 - Inline keyboard symbols font

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https://hg.mozilla.org/integration/gaia-1_4/rev/a2a652a55b32
Author: Ryan VanderMeulen <rvandermeulen@mozilla.com>
Desc: Merge pull request #20718 from crh0716/995458_v1.4

Bug 995458 - Only calls the last callback of an async operation r=jaoo, a=1.4+

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https://hg.mozilla.org/integration/gaia-1_4/rev/2e92339e0210
Author: Arthur Chen <crh0716@gmail.com>
Desc: Bug 995458 - Only calls the last callback of an async operation r=jaoo, a=1.4+
Bumping manifests a=b2g-bump