Use correct convention for example name

See https://github.com/dart-lang/site-www/issues/413
diff --git a/README.md b/README.md
index 2e86c22..c3dd4eb 100644
--- a/README.md
+++ b/README.md
@@ -16,7 +16,7 @@
 
 ## Example
 
-See `example/example_server.dart`
+See `example/example.dart`
 
 ```dart
 import 'package:shelf/shelf.dart' as shelf;
diff --git a/example/example_server.dart b/example/example.dart
similarity index 100%
rename from example/example_server.dart
rename to example/example.dart