N°5621 Move showdown 2.0.0-alpha1 to NPM

Current file header is : /*! showdown v 2.0.0-alpha1 - 25-09-2018 */

Official 2.0.0-alpha doesn't match neither on content nor date :(
Considering date we would be at 1.8.7, but it is also quite different (and has vulnerabilities)
In consequence switching to 2.0.0.

node_modules/cliui/index.mjs

@@ -0,0 +1,13 @@
+// Bootstrap cliui with CommonJS dependencies:
+import { cliui } from './build/lib/index.js'
+import { wrap, stripAnsi } from './build/lib/string-utils.js'
+
+export default function ui (opts) {
+  return cliui(opts, {
+    stringWidth: (str) => {
+      return [...str].length
+    },
+    stripAnsi,
+    wrap
+  })
+}