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

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https://hg.mozilla.org/integration/gaia-central/rev/587815922b97
Author: steveck-chung <schung@mozilla.com>
Desc: Merge pull request #20857 from lanahuong/Bug_959201

Bug 959201 - [Messages][Drafts] Wrong Cursor position in the message compose of a Draft. r=steveck-chung

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https://hg.mozilla.org/integration/gaia-central/rev/d98729de4992
Author: Lana Huong Scravaglieri <lana@Naboo-2.local>
Desc: Bug 959201 - [Messages][Drafts] Wrong Cursor position in the message compose of a Draft
Bumping manifests a=b2g-bump