Validator (Editor). Can't load/validate url.

[JohnLukeBentley]

To reproduce:

• Choose [Author-Date].
• Source: "URL". Paste: https://raw.githubusercontent.com/Juris-M/jm-styles/master/jm-indigobook.csl
• Observe the [Load] and [Validate] buttons remain disabled. Clicking on either button does nothing.

Tested in Firefox 59.0.2 and Chrome Version 65.0.3325.181 (Official Build) (64-bit).