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

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https://hg.mozilla.org/integration/gaia-central/rev/8ccdabce7c03
Author: Jose M. Cantera <jmcanterafonseca@gmail.com>
Desc: Merge pull request #15858 from jmcanterafonseca/fix_index_readonly

Bug 966205 - Success callback could be invoked two times in the fb_data_reader module when datastore is readonly

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https://hg.mozilla.org/integration/gaia-central/rev/ba7e8231e0be
Author: Jose M. Cantera <jmcanterafonseca@gmail.com>
Desc: Bug 966205 - Success callback could be invoked two times in the fb_data_reader module when datastore is readonly

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https://hg.mozilla.org/integration/gaia-central/rev/1f1488dff668
Author: Etienne Segonzac <etienne@segonzac.info>
Desc: Merge pull request #15861 from etiennesegonzac/bug-958338-fdn-error-support

Bug 958338 - Proper handling for FdnCheckFailure errors in TelephonyHelper r=ferjm

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https://hg.mozilla.org/integration/gaia-central/rev/eb21b7ebedf0
Author: Etienne Segonzac <etienne@segonzac.info>
Desc: Bug 958338 - Proper handling for FdnCheckFailure errors in TelephonyHelper.
Bumping manifests a=b2g-bump