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

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https://hg.mozilla.org/integration/gaia-central/rev/2b8576720f96
Author: Ryan VanderMeulen <rvandermeulen@mozilla.com>
Desc: Merge pull request #17038 from flodolo/bug975637_ftuselection

Bug 980456 - [B2G][FTE][Date & Time] Continent and city selections aren't displayed highlighted

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https://hg.mozilla.org/integration/gaia-central/rev/4133291d60c4
Author: Francesco Lodolo (:flod) <flod@lodolo.net>
Desc: Bug 980456 - [B2G][FTE][Date & Time] Continent and city selections aren't displayed highlighted

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https://hg.mozilla.org/integration/gaia-central/rev/e9696b59fbae
Author: Ryan VanderMeulen <rvandermeulen@mozilla.com>
Desc: Merge pull request #17014 from flodolo/bug942573_feedbackstring

Bug 942573 - [Settings] Feedback: improve "Thank you" message

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https://hg.mozilla.org/integration/gaia-central/rev/eb19597cd07c
Author: Francesco Lodolo (:flod) <flod@lodolo.net>
Desc: Bug 942573 - [Settings] Feedback: improve wording when feedback is complete

Updated string from :matej
Bumping manifests a=b2g-bump