Tweak travis config

.travis.yml

@@ -1,28 +1,31 @@
 language: rust
-
-rust:
-  - stable
-  - beta
-  - nightly
 sudo: false
-before_script:
-  - pip install 'travis-cargo<0.2' --user && export PATH=$HOME/.local/bin:$PATH
-script:
-  - cargo build
-  - cargo test
-  - cargo doc --no-deps
-  - if [ "$TRAVIS_RUST_VERSION" == "nightly" ]; then cargo bench ; fi
 
-after_success:
-  - travis-cargo --only nightly doc-upload
+matrix:
+  include:
+    - rust: 1.21.0
+    - rust: stable
+    - os: osx
+    - rust: beta
+    - rust: nightly
+
+    - rust: nightly
+      before_script:
+        - pip install 'travis-cargo<0.2' --user && export PATH=$HOME/.local/bin:$PATH
+      script:
+        - cargo doc --no-deps --all-features
+      after_success:
+        - travis-cargo --only nightly doc-upload
+
+script:
+  - cargo test
+
 env:
   global:
     - RUSTFLAGS='--cfg assert_timer_heap_consistent'
     - secure: "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"
 
+
 notifications:
   email:
     on_success: never
-os:
-  - linux
-  - osx