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

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https://hg.mozilla.org/integration/gaia-central/rev/1767087b2506
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Merge pull request #15042 from KevinGrandon/bug_956699_remove_duplicate_css_rules

Bug 956699 - [System] Duplicate css rules for .accessibility-invert

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https://hg.mozilla.org/integration/gaia-central/rev/598b2a4b06d1
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Bug 956699 - [System] Duplicate css rules for .accessibility-invert

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https://hg.mozilla.org/integration/gaia-central/rev/dfd08ddb7637
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Merge pull request #15019 from KevinGrandon/bug_956393_suggestion_result_clear_only

Bug 956393 - [Search] Suggestions results are cleared unexpectedly r=amin

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https://hg.mozilla.org/integration/gaia-central/rev/02a7850f6d9c
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Bug 956393 - [Search] Suggestions results are cleared unexpectedly r=amirn