travis: Use rustup provided clippy. (#95)

.travis.yml

@@ -3,7 +3,6 @@ sudo: false
 env:
  global:
  - RUST_BACKTRACE=1
- - CLIPPY_VERSION=0.0.192
  - RUSTFLAGS="-D warnings"
 cache: cargo
 
@@ -17,11 +16,9 @@ matrix:
  - rustup component add rustfmt-preview
  before_script:
  - cargo fmt --all -- --write-mode diff
- # This build uses the nightly used by TiKV and checks clippy.
- - rust: nightly-2018-04-06
+ - rust: nightly
  install:
- - export PATH="$PATH:$HOME/.cargo/bin"
- - if [[ `cargo clippy -- --version` != $CLIPPY_VERSION* ]]; then cargo install -f clippy --version $CLIPPY_VERSION; fi
+ - rustup component add clippy-preview --toolchain nightly
  before_script:
  - cargo clippy