use Rust 1.29

.travis.yml

@@ -1,6 +1,6 @@
 language: rust
 rust:
-    - stable
+    - 1.29.0
 cache:
   cargo: true
   timeout: 1200
@@ -9,24 +9,13 @@ addons:
     packages:
       - unzip
 before_install:
-  # The Rust stable toolchain is already installed, ${RUST_NEXT} is added to
-  # provide `cargo clippy` and `cargo fmt`.
-  - rustup toolchain install ${RUST_NEXT}
-  - rustup component add --toolchain=${RUST_NEXT} rustfmt-preview clippy-preview
-  # Some symlinking is still necessary for clippy to function properly.
-  - ln -sf ${HOME}/.rustup/toolchains/${RUST_NEXT}-x86_64-unknown-linux-gnu/bin/clippy-driver ${HOME}/.rustup/toolchains/${RUST_NEXT}-x86_64-unknown-linux-gnu/bin/cargo-clippy $HOME/.cargo/bin/
+  - rustup component add --toolchain=${TRAVIS_RUST_VERSION} rustfmt-preview clippy-preview
 env:
   global:
     - RUST_BACKTRACE=1
     # Enables additional cpu-specific optimizations.
     - RUSTFLAGS="-D warnings -C target-cpu=native"
-    # Note: `beta` should be removed along with `RUST_NEXT` after the 1.28
-    #       stable release on 2018-09-13.
-    - RUST_NEXT=beta
 script:
-  - cargo +${RUST_NEXT} clippy -- --deny clippy
-  - cargo +${RUST_NEXT} clippy --tests --examples --benches -- --deny clippy
-  - cargo +${RUST_NEXT} clippy --all-features -- --deny clippy
-  - cargo +${RUST_NEXT} clippy --all-features --tests -- --deny clippy
-  - cargo +${RUST_NEXT} fmt -- --check
+  - cargo clippy --tests --examples --benches -- --deny clippy
+  - cargo fmt -- --check
   - cargo test --all-features --release