Bumping gaia.json for 1 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-1_4/rev/4855c3e6ca4d
Author: Michael Henretty <michael.henretty@gmail.com>
Desc: Merge pull request #17997 from mikehenrty/bug-988737-clear

Bug 988737 - SMS notifications do not clear when launching SMS app after... r=alive
Bumping manifests a=b2g-bump