bump Go to 1.3

~~Requires #6539~~ merged
~~Requires #6684~~ merged
~~Requires #6913~~ merged
~~Requires #7170~~ merged
Fixes #4983
Some cli integration tests are still failing with this branch.
It's done: https://github.com/unclejack/docker/commit/31c4dc295fab950426be5ef855ed6feb50363e19

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