Merge pull request #182 from cwall-dev/fix/important-lost-unkownvalues

BugFix: Important get's lost in case of Unknown Values.

src/ExCSS/Parser/StylesheetComposer.cs

@@ -657,6 +657,7 @@ public Property CreateDeclarationWith(Func<string, Property> createProperty, ref
 
                             property = new UnknownProperty(propertyName);
                             property.TrySetValue(value);
+                            property.IsImportant = important;
                             _nodes.Push(property);
                         }
                     }