Improve contrast for .wdn-button-complement #702

According to snook.ca's [Colour Contrast Check](http://snook.ca/technical/colour_contrast/colour.html), this was already WCAG 2 AA Compliant. [HTML_CodeSniffer](http://squizlabs.github.io/HTML_CodeSniffer/) recommended that it be changed from #008a2c to #00892c. The visual difference is negligible so change it we shall.

fixes #702