Fix Usage Docs Example (JedWatson#1799)

Before this change, console log in browser will throw
> Selected: [object Object]

After this change console log in browser will throw some nice information.
> Selected: {"value":"three","label":"Three"}

Author: rohmanhm

README.md

@@ -83,7 +83,7 @@ var options = [
 ];
 
 function logChange(val) {
-  console.log("Selected: " + val);
+  console.log("Selected: " + JSON.stringify(val));
 }
 
 <Select