message: Try fixing the build script.
  The problem is discovered and discussed in
diff: @@ -24,11 +24,11 @@ env:
  - FEATURES='hdr'
  script:
  - if [ -z "$FEATURES" ]; then
  - cargo build -v;
  - if [ "$TRAVIS_RUST_VERSION" = "nightly" ]; then cargo test -v; fi;
  + cargo build -v &&
  + if [ "$TRAVIS_RUST_VERSION" = "nightly" ]; then cargo test -v; fi &&
  cargo doc -v;
  else
  - cargo build -v --no-default-features --features "$FEATURES";
  - if [ "$TRAVIS_RUST_VERSION" = "nightly" ]; then cargo test -v --no-default-features --features "$FEATURES"; fi;
  + cargo build -v --no-default-features --features "$FEATURES" &&
  + if [ "$TRAVIS_RUST_VERSION" = "nightly" ]; then cargo test -v --no-default-features --features "$FEATURES"; fi &&
  cargo doc -v;
  fi
  