fix CHANGELOG date

Signed-off-by: Victor Vieux <[email protected]>

bump version to 1.13.1

Signed-off-by: Victor Vieux <[email protected]>

bump version to 1.13.1-rc2

Signed-off-by: Victor Vieux <[email protected]>

bump version to 1.13.0-rc7

Signed-off-by: Victor Vieux <[email protected]>

Merge pull request moby#71 from mlaventure/bump-1.12.6

Bump version to 1.12.6