v2.2.0

This version includes fixes for many of the Web Platform Tests and pre-transpiles code so that no polyfills or conversion is needed for IE11 and other older browsers.

• No longer observes non-replaced inline elements (#57).
• Supports different writing modes and returns correct values for inline/block sizes (#59).
• Scope change: observer.callback.this = observer (#58).
• Library is now pre-transpiled to ES5. Modules are still ESM (#39).