Disable fuzzy auto-linking of URLs in markdown preview (#884)

refs https://github.com/TryGhost/Ghost/issues/8987

- set `linkify-it` `fuzzyLink` option to false so that it only auto-links URLs starting with `http(s)://` or other valid schemes

ghost/admin/app/utils/format-markdown.js

@@ -40,7 +40,6 @@ let markdownitNamedHeaders = function markdownitNamedHeaders(md) {
     };
 };
 
-// eslint-disable-next-line new-cap
 let md = markdownit({
     html: true,
     breaks: true,
@@ -51,6 +50,11 @@ let md = markdownit({
     .use(markdownitMark)
     .use(markdownitNamedHeaders);
 
+// configure linkify-it
+md.linkify.set({
+    fuzzyLink: false
+});
+
 export default function formatMarkdown(_markdown, replaceJS = true) {
     let markdown = _markdown || '';
     let escapedhtml = '';