fix: banner missing

Author: hilongjw

build.js

@@ -1,4 +1,3 @@
-const fs = require('fs')
 const path = require('path')
 const rollup = require('rollup')
 const babel = require('rollup-plugin-babel')
@@ -21,6 +20,7 @@ async function build (options, _outputOptions) {
     const outputOptions = {
       format: _outputOptions.format,
       exports: 'named',
+      banner: banner,
       file: path.resolve(__dirname, _outputOptions.filename),
       name: 'VueLazyload'
     }

vue-lazyload.esm.js

@@ -1,3 +1,9 @@
+/*!
+ * Vue-Lazyload.js v1.3.4
+ * (c) 2021 Awe <hilongjw@gmail.com>
+ * Released under the MIT License.
+ */
+
 /*!
  * is-primitive <https://github.com/jonschlinkert/is-primitive>
  *