Font fallback on Edge because of missing MIME type

[timsneath]

On Edge, the embedded fonts used for charts aren't rendering correctly, but are falling back to a default. This seems to be because the MIME type isn't specified for the stylesheet references in highchart.js and highchart2.js.

On Edge 40:

On Chrome 57:

Per the HTML5 standard for the link element, a type is not required, but if it is specified, "the value must be a valid MIME type".

[jbkunst]

@timsneath,

Oh, my fault! I forgot add the MIME type. Thank you very much.

PR accpeted.

[jbkunst]

closed in #309

[timsneath]

Thanks so much!

[jbkunst]

No! Thanks to YOU!