Enable HTML tags to make Mermaid render dotted lines

Flowcharts appear to be missing styles if HTML tags are disabled
for flowchart labels. They appear to disabled because some browsers
mermaid-js/mermaid#303 may omit labels
if they are present, but in testing with Microsoft Edge this
doesn't appear to be an issue now.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/60869

app/assets/javascripts/behaviors/markdown/render_mermaid.js

@@ -31,7 +31,7 @@ export default function renderMermaid($els) {
         // mermaidAPI options
         theme: 'neutral',
         flowchart: {
-          htmlLabels: false,
+          htmlLabels: true,
         },
       });