If you receive the message when publishing your hex package:

Docs successfully generated.
View them at "doc/index.html".
Local password: 
Publishing package...
[#########################] 100%
** (ArgumentError) argument error
    (stdlib) :io.put_chars(:standard_io, :unicode, [[[], <<80, 97, 99, 107, 97, 103, 101, 32, 112, 117, 98, 108, 105, 115, 104, 101, 100, 32, 116, 111, 32, 104, 116, 116, 112, 115, 58, 47, 47, 104, 101, 120, 46, 112, 109, 47, 112, 97, 99, 107, 97, 103, 101, 115, 47, 101, 120, 95, ...>>], 10])

Upgrade to the newest hex 0.17.3.

The issue is in pull request #489

To upgrade, run:

mix local.hex

You should see something like this:

Found existing entry: /Users/cj/.kiex/mix/archives/elixir-1.5.3/hex-0.17.2
Are you sure you want to replace it with "https://repo.hex.pm/installs/1.5.0/hex-0.17.3.ez"? [Yn] y
* creating /Users/cj/.kiex/mix/archives/elixir-1.5.3/hex-0.17.3

Then rerun:

mix hex.publish