fix: merge highlight options with `defu` (#409)

fix: merge highlight options with `defu` (#409) · nuxt-content/mdc@babd9f1

Original file line number	Diff line number	Diff line change
`@@ -53,10 +53,7 @@ export const createParseProcessor = async (inlineOptions: MDCParseOptions = {})`
`53`	`53`	`if (inlineOptions.highlight === false) {`
`54`	`54`	`delete options.rehype.plugins.highlight`
`55`	`55`	`} else {`
`56`		`-options.rehype.plugins.highlight.options = {`
`57`		`- ...(options.rehype.plugins.highlight.options \|\| {}),`
`58`		`- ...(options.highlight \|\| {})`
`59`		`-}`
	`56`	`+options.rehype.plugins.highlight.options = defu({}, options.rehype.plugins.highlight.options, options.highlight \|\| {})`
`60`	`57`	`}`
`61`	`58`	`}`
`62`	`59`