Fixed broken URL. Fixes #111.

[nbianca]

No description provided.

[rust-highfive]

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[John-Steidley]

I think that we should use the link to 1.3's version of the documentation (https://doc.rust-lang.org/1.3.0/std/thread/fn.scoped.html) which has a deprecation notice and is the most up to date version of the documentation that exists in the standard library.

[brson]

Thanks!