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

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https://hg.mozilla.org/integration/gaia-central/rev/64a10d91715c
Author: Zac <zcampbell@mozilla.com>
Desc: Merge pull request #13256 from bebef1987/fix_char

Bug 933181 - UnicodeDecodeError in XML report generation

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https://hg.mozilla.org/integration/gaia-central/rev/68113826d60d
Author: Bebe <bebe@mozilla.ro>
Desc: Bug 933181 - UnicodeDecodeError in XML report generation