Added keywords (#707)

[lucashorward]

Make sure these boxes are checked! 📦✅

• You have the latest version of rustfmt installed

$ rustup component add rustfmt

• You ran cargo fmt on the code base before submitting
• You reference which issue is being closed in the PR text

✨✨ 😄 Thanks so much for contributing to wasm-pack! 😄 ✨✨

Closes #707

package.json files usually contain a keywords array so that npm can make searching easier. Currently the keywords from the Cargo.toml are not exported to the package.json, meaning they have to be done manually before a package is published to npm, or be difficult to find on npm.

This is my first edit, so please let me know if I have made some junior mistakes

[lucashorward]

The test is failing for build_with_and_without_wasm_bindgen_debug - but when I run cargo test on master, this failure is also there..
Do I have a wrong configuration setting or something?

[Pauan]

Looks great, thanks!