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

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https://hg.mozilla.org/integration/gaia-2_1/rev/9a6b6c4fb8ee
Author: Salvador de la Puente <salva@unoyunodiez.com>
Desc: Bug 1079479 - [Usage][Cost Control] Remove incorrect message from Mobile App Usage list when Mobile usage is unchecked

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https://hg.mozilla.org/integration/gaia-2_1/rev/bcdf929c2ed1
Author: Salvador de la Puente <salva@unoyunodiez.com>
Desc: Bug 1080611 - [Usage][Cost Control] The amount of data shown in Usage Settings and the chart differ

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https://hg.mozilla.org/integration/gaia-2_1/rev/c67d31c2f5ce
Author: gasolin <gasolin@gmail.com>
Desc: Bug 1075200 - [Settings] Unable to set AM/PM time after change time format

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https://hg.mozilla.org/integration/gaia-2_1/rev/7d49c2c9d58b
Author: Ben Francis <ben@tola.me.uk>
Desc: Bug 1075011 - Swap browser app for search app on old homescreen
Bumping manifests a=b2g-bump