Fixed active link

Author: syrusakbary

docs/pages/_template.js

@@ -14,7 +14,7 @@ class Template extends React.Component {
     return (
       <div>
         <Menu width={200} right>
-            <span><Link to="/playground/">Try it out</Link></span>
+            <span><Link to="/playground/" className={path.indexOf('/playground')==0?"active":null}>Try it out</Link></span>
             <span><Link to="/docs/quickstart/" className={path.indexOf('/docs')==0?"active":null}>Docs</Link></span>
             <span><Link to="/community/">Community</Link></span>
             <a href="https://github.com/graphql-python/graphene/">Github</a>
@@ -26,7 +26,7 @@ class Template extends React.Component {
                     Graphene
                 </Link>
                 <nav className="header-nav">
-                    <Link to="/playground/">Try it out</Link>
+                    <Link to="/playground/" className={path.indexOf('/playground')==0?"active":null}>Try it out</Link>
                     <Link to="/docs/quickstart/" className={path.indexOf('/docs')==0?"active":null}>Docs</Link>
                     <Link to="/community/">Community</Link>
                     <a href="https://github.com/graphql-python/graphene/">Github</a>