Pricing table class names rendered with an apostrophe

Hi
.avia-pricing-row and
.avia-heading-row
are being rendered in Firefox, Chrome and IE11 as

<li class=” ‘avia-pricing-row’ “> content
<li class=” ‘avia-heading-row’ “> content

The class names are have an apostrophe added just before and after the class name.

The result is that the CSS does not work.

When the apostrophes are removed in the inspector in the browsers the CSS does work.

How can we ensure that the apostrophes are not added during rendering of the page?

Visit http://www.zilink.co.uk/subscriptions to see an expample.

Thanks