Merge pull request #408 from red-gate/button--black

Update .button--black

Author: philscott-rg

dist/honeycomb.app.css

@@ -263,6 +263,7 @@ <h1>Honeycomb web toolkit class name cheatsheet</h1>
                     <ul>
                         <li>.button--black</li>
                         <li>.button--buy</li>
+                        <li>.button--dark-grey</li>
                         <li>.button--disabled</li>
                         <li>.button--disabled.button--primary</li>
                         <li>.button--download</li>