update dart images (#32)

* update dart icons
* update the images size reference
diff --git a/example/files/dart.png b/example/files/dart.png
index fd6de2a..96b6373 100644
--- a/example/files/dart.png
+++ b/example/files/dart.png
Binary files differ
diff --git a/example/files/favicon.ico b/example/files/favicon.ico
index e605972..93b0890 100644
--- a/example/files/favicon.ico
+++ b/example/files/favicon.ico
Binary files differ
diff --git a/example/files/index.html b/example/files/index.html
index 7bf28d1..7984de0 100644
--- a/example/files/index.html
+++ b/example/files/index.html
@@ -7,6 +7,6 @@
   </head>
   <body>
     <h1>Hello, shelf_static!</h1>
-    <img src='dart.png' alt='Dart logo' width='150' height='151'>
+    <img src='dart.png' alt='Dart logo' width='152' height='152'>
   </body>
 </html>