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

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https://hg.mozilla.org/integration/gaia-1_4/rev/4c6f5b1ee888
Author: Carsten Book <tomcat@mozilla.com>
Desc: Merge pull request #18718 from azasypkin/bug-995350-save-button

Bug 995350 - [SMS] - Display Save button for attached image file name having hidden directories ".gallery/". r=julien
Bumping manifests a=b2g-bump