Added spec for properties prefixed with a dash

spec/css/dash-prefix.css

@@ -0,0 +1,5 @@
+body {
+  background: green;
+  background-image: -moz-linear-gradient(top, bottom, from(red), to(green));
+  background-image: -webkit-gradient(linear, left top, left bottom, color-stop(0, red), color-stop(1, green));
+}

spec/engine_spec.rb

@@ -30,6 +30,10 @@ def css file
       lessify(:css_3).should == css(:css_3)
     end
 
+    it "should handle properties prefixed with a dash" do
+      lessify(:dash_prefix).should == css(:dash_prefix)
+    end
+
     it "should parse comments" do
       lessify(:comments).should == css(:comments)
     end

spec/less/dash-prefix.less

@@ -0,0 +1,8 @@
+@top_color: red;
+@bottom_color: green;
+
+body {
+  background: @bottom_color;
+  background-image: -moz-linear-gradient(top, bottom, from(@top_color), to(@bottom_color));
+  background-image: -webkit-gradient(linear, left top, left bottom, color-stop(0.00, @top_color), color-stop(1.00, @bottom_color));
+}