Fix serializing currentColor

Fixes parcel-bundler#408

Author: devongovett

node/test/visitor.test.mjs

@@ -944,4 +944,23 @@ test('supports returning raw values as variables', () => {
   assert.equal(res.code.toString(), '.EgL3uq_foo{color:var(--EgL3uq_foo)}');
 });
 
+test('works with currentColor', () => {
+  let res = transform({
+    filename: 'test.css',
+    minify: true,
+    code: Buffer.from(`
+      .foo {
+        color: currentColor;
+      }
+    `),
+    visitor: {
+      Rule(rule) {
+        return rule;
+      }
+    }
+  });
+
+  assert.equal(res.code.toString(), '.foo{color:currentColor}');
+});
+
 test.run();

src/values/color.rs

@@ -73,7 +73,7 @@ impl CurrentColor {
   where
     S: serde::Serializer,
   {
-    serializer.serialize_str("currentcolor")
+    serde::Serialize::serialize(&CurrentColor::CurrentColor, serializer)
   }
 
   fn deserialize<'de, D>(deserializer: D) -> Result<(), D::Error>