message: Simplify .travis.yml according to Travis Rust guide
diff: language: rust
  -cache: cargo
  -
  +rust:
  + - stable
  + - beta
  + - nightly
  matrix:
  - include:
  - # The earliest stable Rust version that works
  - - env: TARGET=x86_64-unknown-linux-gnu
  - rust: 1.24.0
  - - env: TARGET=x86_64-unknown-linux-gnu
  - rust: beta
  - - env: TARGET=x86_64-unknown-linux-gnu
  - rust: nightly
  -
  -
  -notifications:
  - email: false
  + allow_failures:
  + - rust: nightly
  