Fix unpkg url in docs

[mischnic]

See #565

https://unpkg.com/lightningcss-wasm?module imports https://unpkg.com/napi-wasm@^1.0.1?module which responds with

Cannot generate module for napi-wasm@1.1.0/index.mjs

SyntaxError: unknown: Support for the experimental syntax 'classProperties' isn't currently enabled (32:10):

  30 | 
  31 | export class Environment {
> 32 |   scopes = [];
     |          ^
  33 |   referenceId = 1;
  34 |   references = new Map();
  35 |   deferred = [null];

Add @babel/plugin-proposal-class-properties (https://git.io/vb4SL) to the 'plugins' section of your Babel config to enable transformation.

undefined

https://esm.run (= jsdelivr) works fine