update c# interop to use percentage

csharp/Facebook.Yoga/YogaUnit.cs

@@ -0,0 +1,17 @@
+/**
+ * Copyright (c) 2014-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ */
+ 
+namespace Facebook.Yoga
+{
+    public enum YogaUnit
+    {
+        Pixel,
+        Percent
+    }
+}