Merge pull request #16 from epage/clippy

chore: Switch to clippy-preview

Author: epage

.travis.yml

@@ -18,10 +18,10 @@ matrix:
     install:
     script:
     - cargo check --tests --all-features
-  - env: CLIPPY_VERSION="0.0.209"
-    rust: nightly-2018-06-19
+  - env: CLIPPY
+    rust: nightly-2018-07-17
     install:
-      - travis_wait cargo install clippy --version $CLIPPY_VERSION || echo "clippy already installed"
+      - rustup component add clippy-preview
     script:
       - cargo clippy --all-features -- -D clippy