fix: use type check instead of nullish coalescing operator

Author: cossssmin

lib/index.js

@@ -3,7 +3,7 @@ const isUrl = require('is-url-superb')
 const matchHelper = require('posthtml-match-helper')
 
 module.exports = (config = {}) => tree => {
-  config.strict = config.strict ?? true
+  config.strict = typeof config.strict === 'boolean' ? config.strict : true
 
   const process = node => {
     if (!config || !config.parameters) {