Ignore Jekyll wrapping in JS files

**Description of the false positive**

In some cases in Jekyll projects, a JS file may still receive a front-matter heading, which would look incorrect (and to just a JS parser, would indeed be incorrect.) But in this case, I believe the front-matter is necessary.

**URL to the alert on the project page on LGTM.com**

https://lgtm.com/projects/g/mmistakes/minimal-mistakes/snapshot/2d5eb9fb06827645b4bf5d55d96584353159dff0/files/assets/js/lunr/lunr-gr.js?sort=name&dir=ASC&mode=heatmap#x5ea38509661d9a53:1