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/string-width/index.js

@@ -0,0 +1,47 @@
+'use strict';
+const stripAnsi = require('strip-ansi');
+const isFullwidthCodePoint = require('is-fullwidth-code-point');
+const emojiRegex = require('emoji-regex');
+
+const stringWidth = string => {
+	if (typeof string !== 'string' || string.length === 0) {
+		return 0;
+	}
+
+	string = stripAnsi(string);
+
+	if (string.length === 0) {
+		return 0;
+	}
+
+	string = string.replace(emojiRegex(), '  ');
+
+	let width = 0;
+
+	for (let i = 0; i < string.length; i++) {
+		const code = string.codePointAt(i);
+
+		// Ignore control characters
+		if (code <= 0x1F || (code >= 0x7F && code <= 0x9F)) {
+			continue;
+		}
+
+		// Ignore combining characters
+		if (code >= 0x300 && code <= 0x36F) {
+			continue;
+		}
+
+		// Surrogates
+		if (code > 0xFFFF) {
+			i++;
+		}
+
+		width += isFullwidthCodePoint(code) ? 2 : 1;
+	}
+
+	return width;
+};
+
+module.exports = stringWidth;
+// TODO: remove this in the next major version
+module.exports.default = stringWidth;