feat(cli): use clean-css to minify css

packages/vant-cli/src/compiler/compile-css.ts

@@ -1,13 +1,15 @@
 import postcss from 'postcss';
 import postcssrc from 'postcss-load-config';
-import { minify } from 'csso';
+import CleanCss from 'clean-css';
 import { POSTCSS_CONFIG_FILE } from '../common/constant';
 
+const cleanCss = new CleanCss();
+
 export async function compileCss(source: string | Buffer) {
   const config = await postcssrc({}, POSTCSS_CONFIG_FILE);
   const { css } = await postcss(config.plugins as any).process(source, {
     from: undefined
   });
 
-  return minify(css).css;
+  return cleanCss.minify(css).styles;
 }