message: On CI only use mdbook 0.1.7.
diff: @@ -6,14 +6,6 @@ dist: trusty
  git:
  depth: 1
  -# Using 'cache: cargo' to cache target/ and all of $HOME/.cargo/
  -# doesn't work well: the cache is large and it takes several minutes
  -# to move it to and from S3. So instead we only cache the mdbook
  -# binary.
  -cache:
  - directories:
  - - $HOME/.cargo/bin/
  -
  matrix:
  include:
  - env: TARGET=x86_64-unknown-linux-gnu
  @@ -48,7 +40,7 @@ matrix:
  ALT=i686-unknown-linux-gnu
  rust: nightly
  install:
  - - mdbook --help || cargo install mdbook --force
  + - travis_retry curl -Lf https://github.com/rust-lang-nursery/mdBook/releases/download/v0.1.7/mdbook-v0.1.7-x86_64-unknown-linux-gnu.tar.gz | tar -xz --directory=$HOME/.cargo/bin
  script:
  - cargo test --features=deny-warnings
  - cargo doc --no-deps
  