refactor viewBox for svg

lib/attributes.js

@@ -41,6 +41,15 @@ function fontAndLinesDiffer(a, b) {
     return arrayDiffer(a.lines, b.lines);
 }
 
+const ViewBoxAttributes = {
+    minX: true,
+    minY: true,
+    vbWidth: true,
+    vbHeight: true,
+    align: true,
+    meetOrSlice: true
+};
+
 const NodeAttributes = {
     name: true,
     transform: {
@@ -180,5 +189,6 @@ export {
     UseAttributes,
     RenderableOnlyAttributes,
     LinearGradientAttributes,
-    RadialGradientAttributes
+    RadialGradientAttributes,
+    ViewBoxAttributes
 };