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

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https://hg.mozilla.org/integration/gaia-1_4/rev/bce3e456dc11
Author: Ryan VanderMeulen <rvandermeulen@mozilla.com>
Desc: Merge pull request #21046 from arcturus/bug-987966

[DO NOT MERGE YET] Bug 987966 - [contacts] placeholder for date fields in add/edit mode is always in English: 'Date'

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https://hg.mozilla.org/integration/gaia-1_4/rev/763913f5d3b6
Author: Francisco Jordano <arcturus@ardeenelinfierno.com>
Desc: Bug 987966 - [contacts] placeholder for date fields in add/edit mode is always in English: 'Date'
Bumping manifests a=b2g-bump