Fix @font-face issue

- `css-parse` didn't support @font-face before 2.0
  –> fixed

lib/convert/css.js

@@ -75,6 +75,8 @@ Converter.prototype.visit = function(node){
     case 'supports':
       var name = node.type[0].toUpperCase() + node.type.slice(1);
       return this['visit' + name](node);
+    case 'font-face':
+      return this.visitFontFace(node);
   }
 };
 
@@ -94,6 +96,25 @@ Converter.prototype.visitRules = function(node){
   return buf;
 };
 
+/**
+ * Visit FontFace `node`.
+ *
+ * @param {FontFace} node
+ * @return {String}
+ * @api private
+ */
+
+ Converter.prototype.visitFontFace = function(node){
+   var buf = this.indent + '@font-face';
+   buf += '\n';
+   ++this.indents;
+   for (var i = 0, len = node.declarations.length; i < len; ++i) {
+     buf += this.visitDeclaration(node.declarations[i]);
+   }
+   --this.indents;
+   return buf;
+ };
+
 /**
  * Visit Media `node`.
  *