Allow running tests using "npm test"

The small addition to package.json allows for running tests with `npm test`, rather than `jasmine-node spec`

```
danielstjules:~/GitHub/rhom (scripts-test)
$ npm test

> rhom@0.0.0 test /Users/danielstjules/GitHub/rhom
> ./node_modules/.bin/jasmine-node spec

.............

Finished in 2.168 seconds
13 tests, 33 assertions, 0 failures, 0 skipped
```

Awesome lib btw :)