Bumping gaia.json for 4 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/4b491e58fb7e
Author: Zac <zcampbell@mozilla.com>
Desc: Merge pull request #16286 from viorelaioia/bug_972771

Bug 972771 - Fix failure in test_gallery_delete_image.py

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https://hg.mozilla.org/integration/gaia-central/rev/35ac07d4b03c
Author: Viorela Ioia <viorelaioia@gmail.com>
Desc: Bug 972771 - Fix failure in test_gallery_delete_image.py

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https://hg.mozilla.org/integration/gaia-central/rev/de693afa9727
Author: David Flanagan <dflanagan@mozilla.com>
Desc: Merge pull request #15521 from huchengtw-moz/gallery/Bug_831890-crop-handles-missing

Bug 831890 - [B2G][GALLERY] Crop Handles (Markers) disappear after chang... r=djf

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https://hg.mozilla.org/integration/gaia-central/rev/58a0382ce514
Author: John Hu <johu@mozilla.com>
Desc: Bug 831890 - [B2G][GALLERY] Crop Handles (Markers) disappear after changing orientations.
Bumping manifests a=b2g-bump