Try fixing OSX builds
Try fixing OSX builds

... that I broke by introducing travis-cargo.

SingingTree/rustfmt,aidancully/rust,aidancully/rust,Emilgardis/rustfmt,rust-lang/rustfmt,aidancully/rust,graydon/rust,SingingTree/rustfmt,Emilgardis/rustfmt,aidancully/rust,graydon/rust,studoot/rustfmt,graydon/rust,aidancully/rust,graydon/rust,graydon/rust,rust-lang/rustfmt,flutterhash/rustfmt,graydon/rust,aidancully/rust,studoot/rustfmt