rsvm ls fails to show 1.16.0

[mcandre]

When Rust version 1.16.0 is installed via rsvm install 1.16.0, rsvm ls continues to complain that there are "no" installed versions.

[d3m3vilurr]

can you share system information?

• shell type(zsh or bash)
• shell version
• os type(linux, osx or ...)

in my system, looks haven't any problem.

[d3m3vilurr]

Copy from #36
Host: macOS 10.12.3 Sierra, rsvm 0.5.1.