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

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https://hg.mozilla.org/integration/gaia-central/rev/42600dd249d9
Author: Ryan VanderMeulen <rvandermeulen@mozilla.com>
Desc: Merge pull request #18084 from azasypkin/bug-946497-stretched-thumbnails

Bug 946497 - [B2G][SMS][MMS] Thumbnail previews for cropped images in MMS message appear stretched causing not all of the image to be visible.

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https://hg.mozilla.org/integration/gaia-central/rev/97c34122a9d7
Author: Aleh Zasypkin <azasypkin@mozilla.com>
Desc: Bug 946497 - [B2G][SMS][MMS] Thumbnail previews for cropped images in MMS message appear stretched causing not all of the image to be visible.
Bumping manifests a=b2g-bump