message: Build doc with relevant feaures flags.
  As suggested by .
diff: @@ -30,5 +30,5 @@ script:
  else
  cargo build -v --no-default-features --features "$FEATURES" &&
  if [ "$TRAVIS_RUST_VERSION" = "nightly" ]; then cargo test -v --no-default-features --features "$FEATURES"; fi &&
  - cargo doc -v;
  + cargo doc -v --no-default-features --features "$FEATURES";
  fi
  