Implement installation using trust

.travis.yml

@@ -1,30 +1,26 @@
 language: rust
 
-env:
-  - RUSTFLAGS="-D warnings"
-
 matrix:
   fast_finish: true
   include:
     - rust: nightly
       os: linux
-      env: BUILD_DOCS=1 BUILD_BOOK=1
+      env: RUSTFLAGS="-D warnings" BUILD_DOCS=1 BUILD_BOOK=1
     - rust: nightly
       os: osx
       osx_image: xcode9.2
-      env: BUILD_DOCS=1
+      env: RUSTFLAGS="-D warnings" BUILD_DOCS=1
     - rust: nightly-x86_64-pc-windows-msvc
       os: windows
+      env: RUSTFLAGS="-D warnings"
 
 before_script:
   - rustup component add rustfmt
-  - (test -x $HOME/.cargo/bin/cargo-install-update || cargo install cargo-update)
-  - (test -x $HOME/.cargo/bin/mdbook || cargo install --vers "^0.3" mdbook)
-  - cargo install-update -a
+  - if   [[ -n "$BUILD_BOOK" ]]; then (test -x $HOME/.cargo/bin/mdbook || ./ci/install-mdbook.sh); fi
 
 script:
-  - if ![[ -n "$BUILD_BOOK" ]]; then cargo check --all --benches --bins --examples --tests && cargo test --all; fi
-  - if  [[ -n "$BUILD_BOOK" ]]; then cargo test  --all --benches --bins --examples --tests; fi
+  - if ! [[ -n "$BUILD_BOOK" ]]; then cargo check --all --benches --bins --examples --tests && cargo test --all; fi
+  - if   [[ -n "$BUILD_BOOK" ]]; then cargo test  --all --benches --bins --examples --tests; fi
   - cargo fmt --all -- --check
-  - if  [[ -n "$BUILD_DOCS" ]]; then cargo doc --features docs; fi
-  - if  [[ -n "$BUILD_BOOK" ]]; then mdbook build docs && mdbook test -L ./target/debug/deps docs; fi
+  - if   [[ -n "$BUILD_DOCS" ]]; then cargo doc --features docs; fi
+  - if   [[ -n "$BUILD_BOOK" ]]; then mdbook build docs && mdbook test -L ./target/debug/deps docs; fi

ci/install-mdbook.sh

@@ -0,0 +1,19 @@
+set -euxo pipefail
+
+# Based on the Rust-Embedded WG's book CI
+# https://github.com/rust-embedded/book/blob/master/ci/install.sh
+
+main() {
+    # Note - this will only accept releases tagged with v0.3.x
+    local tag=$(git ls-remote --tags --refs --exit-code \
+                    https://github.com/rust-lang-nursery/mdbook \
+                        | cut -d/ -f3 \
+                        | grep -E '^v0\.3\.[0-9]+$' \
+                        | sort \
+                        | tail -n1)
+
+    curl -LSfs https://japaric.github.io/trust/install.sh | \
+        sh -s -- --git rust-lang-nursery/mdbook --tag $tag
+}
+
+main