Console error on documentation pages.

[mikelittle]

When loading the documentation pages in the dashboard. A console error is displayed.

Uncaught TypeError: t[(t.length - 1)] is undefined
    u highlightjs-line-numbers.min.js:97
    d highlightjs-line-numbers.min.js:93
    s highlightjs-line-numbers.min.js:76
    setTimeout handler*g highlightjs-line-numbers.min.js:145
    s highlightjs-line-numbers.min.js:75
    l highlightjs-line-numbers.min.js:68
    i highlightjs-line-numbers.min.js:61
    i highlightjs-line-numbers.min.js:60
    <anonymous> script.js:2
2 highlightjs-line-numbers.min.js:97:16

It's worth noting the script in question is quite old (version v9.15.6) and there are newer versions. Releases list.

The syntax highlighting still seems to work fine.

Steps to reproduce:

1. Load a documentation page in the dashboard
2. Check the JS console in the browser.

The page should show correctly and there should be no errors in the console.

Acceptance criteria:

• The page should show correctly without errors in the console