Bumping gaia.json for 2 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-1_4/rev/619485e7d626
Author: Ryan VanderMeulen <rvandermeulen@mozilla.com>
Desc: Merge pull request #20250 from eliperelman/bug-974381-homescreen-lag

Bug 974381 - Removing transition phase to improve responsiveness of homescreen edit mode

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https://hg.mozilla.org/integration/gaia-1_4/rev/d538c2023e3b
Author: Eli Perelman <eli@eliperelman.com>
Desc: Bug 974381 - Removing transition phase to improve responsiveness of homescreen edit mode
Bumping manifests a=b2g-bump