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

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https://hg.mozilla.org/integration/gaia-central/rev/f7c5f36c6a0c
Author: Zac <zcampbell@mozilla.com>
Desc: Merge pull request #17557 from zacc/bug_983684

Bug 983684 - Detect device/b2g type and set gaiatest timeout as appropri...

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https://hg.mozilla.org/integration/gaia-central/rev/85f35849d338
Author: Zac <zcampbell@mozilla.com>
Desc: Bug 983684 - Detect device/b2g type and set gaiatest timeout as appropriate r=davehunt

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https://hg.mozilla.org/integration/gaia-central/rev/99fa240b66f8
Author: Zac <zcampbell@mozilla.com>
Desc: Merge pull request #18786 from zacc/bug_1003089

Bug 1003089 - Skip test_receive_call.py if the Plivo credentials are not...

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https://hg.mozilla.org/integration/gaia-central/rev/25ac8c96b4b0
Author: Zac <zcampbell@mozilla.com>
Desc: Bug 1003089 - Skip test_receive_call.py if the Plivo credentials are not present
Bumping manifests a=b2g-bump