Fix example in 13.3

[ejholmes]

Before this fix, compiling produced the following error:

main.rs:3:24: 3:52 error: binary operation + cannot be applied to type `&static/str`
main.rs:3 fn main() { io::println("hello " + world::explore()); }
                                  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
error: aborting due to previous error

[catamorphism]

Thanks! can you remove the {.xfail-test} directive as well? (That was keeping this test from being compiled when the build process extracts tests from the docs, but now we don't need it since you've fixed the example.)

[ejholmes]

Will do, do you want this on the incoming branch as well?

[catamorphism]

Yes, see https://github.com/mozilla/rust/wiki/Note-development-policy (though we could do a better job of making that page easier to find...)

[ejholmes]

Indeed, might I suggest adding a CONTRIBUTING.md file in the root? GitHub will make it visible in the header when someone starts opening a new PR.

[catamorphism]

Good idea -- I opened #4273 to do that.