support arm64 architecture

[longquan7]

I want to build this image on arm64 architecture,but I don't know this file whether or not support arm64 architecture with https://julialang-s3.julialang.org/bin/linux/arm/0.6/julia-0.6.0-pre.beta-linux-arm.tar.gz.

[tianon]

See #15 -- currently, only amd64, arm32v7, and i386 are supported by Julia upstream, but ppc64le and arm64v8 are currently in development (and might show up with a future release).

[longquan7]

@tianon OK,thanks