Fix the build on travis OSX

Author: alexcrichton

.travis.yml

@@ -5,6 +5,8 @@ rust:
   - nightly
 sudo: false
 install:
+  - if [ "$TRAVIS_OS_NAME" = "linux" ]; then OS=unknown-linux-gnu; else OS=apple-darwin; fi
+  - export TARGET=$ARCH-$OS
   - curl -sO https://static.rust-lang.org/dist/rust-$TRAVIS_RUST_VERSION-$TARGET.tar.gz
   - tar xf rust-$TRAVIS_RUST_VERSION-$TARGET.tar.gz
   - rm -rf $HOME/rust/lib/rustlib/$TARGET
@@ -28,8 +30,8 @@ env:
   global:
     secure: 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
   matrix:
-    - TARGET=x86_64-unknown-linux-gnu
-    - TARGET=i686-unknown-linux-gnu
+    - ARCH=x86_64
+    - ARCH=i686
 
 os:
   - linux