doc: fix code for hello world example

[fsouza]

This change closes #2986.

[z0w0]

You seem to be using the stable 0.3.1 release which has the old style of strings. Recently Rust was changed so that all plain str values should be ~str. So the current documentation is correct for the version of Rust I'm using (the latest HEAD from here) however it's not for your version. The documentation for your version is at http://dl.rust-lang.org/doc/0.3/tutorial.html. e.g. this patch fails to build for me:

a.rs:1:16: 1:19 error: bare `str` is not a type
a.rs:1 fn main(args: ~[str]) {
                       ^~~
a.rs:2:16: 2:45 error: binary operation + cannot be applied to type `str/18`
a.rs:2     io::println("hello world from '" + args[0] + "'!");
                       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
a.rs:2:16: 2:53 error: binary operation + cannot be applied to type `str/18`
a.rs:2     io::println("hello world from '" + args[0] + "'!");
                       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

However the current version does. It is kind of awkward for the documentation links to lead to the latest documentation rather than the latest stable, so maybe that should be changed.

[fsouza]

Hi @z0w0. Sorry about that, I should checked this at master.

I think the problem with the tutorial is that in Installation it teaches how to install rust 0.3, and then teaches code that works only with the latest code (master).

May I open an issue for this?