Fix Processor instance in postcssed object

lib/processor.js

@@ -19,8 +19,10 @@ export default class Processor {
         for ( let i of plugins ) {
             let type = typeof i;
             if ( (type === 'object' || type === 'function') && i.postcss ) {
-                normalized.push(i.postcss);
-            } else if ( type === 'object' && Array.isArray(i.plugins) ) {
+                i = i.postcss;
+            }
+
+            if ( typeof i === 'object' && Array.isArray(i.plugins) ) {
                 normalized = normalized.concat(i.plugins);
             } else {
                 normalized.push(i);

test/processor.js

@@ -44,6 +44,14 @@ describe('Processor', () => {
             expect(processor.plugins).to.eql([a]);
         });
 
+        it('adds new processors from object', () => {
+            let a = () => 1;
+            let processor = new Processor();
+            let other     = new Processor([a]);
+            processor.use({ postcss: other });
+            expect(processor.plugins).to.eql([a]);
+        });
+
         it('returns itself', () => {
             let a = () => 1;
             let b = () => 2;