Auto merge of #4635 - dethoter:4430, r=alexcrichton
authorbors <bors@rust-lang.org>
Tue, 17 Oct 2017 17:32:27 +0000 (17:32 +0000)
committerbors <bors@rust-lang.org>
Tue, 17 Oct 2017 17:32:27 +0000 (17:32 +0000)
Fix a documentation for package.build option.

Fix for #4430.


Trivial merge