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

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https://hg.mozilla.org/integration/gaia-central/rev/cc70d60b7bdc
Author: Francisco Jordano <arcturus@ardeenelinfierno.com>
Desc: Merge pull request #16522 from arcturus/bug-973661

Bug 973661 - [FTE] In FTE, when skipping PIN screen, there is no option to get that screen again when pressing back

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https://hg.mozilla.org/integration/gaia-central/rev/dd2c575455e1
Author: Francisco Jordano <arcturus@ardeenelinfierno.com>
Desc: Bug 973661 - [FTE] In FTE, when skipping PIN screen, there is no option to get that screen again when pressing back

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https://hg.mozilla.org/integration/gaia-central/rev/96fd0c5057b6
Author: Hubert Figuière <hub@figuiere.net>
Desc: Merge pull request #16451 from stasm/974361-arr-undefined

Bug 974361 - Memory average assumes the array of measurements always exists r=hub

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https://hg.mozilla.org/integration/gaia-central/rev/e14022e2d19f
Author: Staś Małolepszy <stas@mozilla.com>
Desc: Bug 974361 - Memory average assumes the array of measurements always exists
Bumping manifests a=b2g-bump