Fix ansi_code_example (dart-lang/io#14)

pkgs/io/example/ansi_code_example.dart

diff --git a/pkgs/io/example/ansi_code_example.dart b/pkgs/io/example/ansi_code_example.dart
index 9673b71..255bd72 100644
--- a/pkgs/io/example/ansi_code_example.dart
+++ b/pkgs/io/example/ansi_code_example.dart
@@ -8,7 +8,7 @@
 
 /// Prints a sample of all of the `AnsiCode` values.
 void main() {
-  if (ansiOutputEnabled) {
+  if (!ansiOutputEnabled) {
     print('`ansiOutputEnabled` is `false`.');
     print("Don't expect pretty output.");
   }