update bootstrap to version 4.3.1

vendor/twbs/bootstrap/build/banner.js

@@ -0,0 +1,14 @@
+'use strict'
+
+const pkg = require('../package.json')
+const year = new Date().getFullYear()
+
+function getBanner(pluginFilename) {
+  return `/*!
+  * Bootstrap${pluginFilename ? ` ${pluginFilename}` : ''} v${pkg.version} (${pkg.homepage})
+  * Copyright 2011-${year} ${pkg.author}
+  * Licensed under MIT (https://github.com/twbs/bootstrap/blob/master/LICENSE)
+  */`
+}
+
+module.exports = getBanner