update remaining Go versions to 1.5.4

Some Dockerfiles were missed during update to
1.5.4. This changes those Dockerfiles.

Note that Dockerfile.armhf is not yet updated; it
currently uses Dave Cheney's unofficial ARM builds,
which are marked "end of life", so added a TODO
instead.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>