Adding 'js' to slappey language

[booleans-oss]

fix to #43

It is not a really important change as it allows users with v.2.0.0 slappey.json to still generate commands/events.

The main difference is the change from language === "javascript" to allow "js" by doing so ["javascript", "js"].includes(language). However, the target version for Typescript (ES6) doesn't support polyfills (includes) so I had to add the modules

"lib": [
      "dom",
      "es7"
   ]