Bumping gaia.json for 5 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/a9c51a635e98
Author: James Lal <james@lightsofapollo.com>
Desc: Merge pull request #19634 from lightsofapollo/global-venv

Bug 1015056 - Use global venv for all travis ci tests to simplify python...

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https://hg.mozilla.org/integration/gaia-central/rev/a31172515519
Author: James Lal <james@lightsofapollo.com>
Desc: Add venv source for local ./bin/ci runs

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https://hg.mozilla.org/integration/gaia-central/rev/7a8ca1b47ebc
Author: James Lal <james@lightsofapollo.com>
Desc: add venv to install for gaia_ui_tests

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https://hg.mozilla.org/integration/gaia-central/rev/3c5438bc44c1
Author: James Lal <james@lightsofapollo.com>
Desc: only perform setup once

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https://hg.mozilla.org/integration/gaia-central/rev/a147ceac2925
Author: James Lal <james@lightsofapollo.com>
Desc: Bug 1015056 - Use global venv for all travis ci tests to simplify python package setup
Bumping manifests a=b2g-bump