fix readme (dart-lang/io#70)

pkgs/io/README.md

diff --git a/pkgs/io/README.md b/pkgs/io/README.md
index dc807eb..4ed2e2d 100644
--- a/pkgs/io/README.md
+++ b/pkgs/io/README.md
@@ -26,26 +26,26 @@
 
 ```dart
 /// Runs `dartfmt` commands and `pub publish`.
-Future<Null> main() async {
-  final manager = new ProcessManager();
-  
+Future<void> main() async {
+  final manager = ProcessManager();
+
   // Runs dartfmt --version and outputs the result via stdout.
   print('Running dartfmt --version');
   var spawn = await manager.spawn('dartfmt', ['--version']);
   await spawn.exitCode;
-  
+
   // Runs dartfmt -n . and outputs the result via stdout.
   print('Running dartfmt -n .');
   spawn = await manager.spawn('dartfmt', ['-n', '.']);
   await spawn.exitCode;
-  
+
   // Runs pub publish. Upon hitting a blocking stdin state, you may directly
   // output to the processes's stdin via your own, similar to how a bash or
   // shell script would spawn a process.
   print('Running pub publish');
   spawn = await manager.spawn('pub', ['publish']);
   await spawn.exitCode;
-  
+
   // Closes stdin for the entire program.
   await sharedStdIn.terminate();
 }