fix: improve css regex for preprocessors (#18)

Author: antfu

src/utils.ts

@@ -1,7 +1,7 @@
 const IS_JS_RE = /\.[cm]?js(\?[^.]+)?$/
 const IS_MODULE_RE = /\.mjs(\?[^.]+)?$/
 const HAS_EXT_RE = /[^./]+\.[^./]+$/
-const IS_CSS_RE = /\.css(\?[^.]+)?$/
+const IS_CSS_RE = /\.(css|postcss|sass|scss|less|stylus|styl)(\?[^.]+)?$/
 
 export function isJS (file: string) {
   return IS_JS_RE.test(file) || !HAS_EXT_RE.test(file)