Fix bad reference in string interpolation.

dart/sdk/lib/_internal/compiler/implementation/scanner/scanner.dart

Index: dart/sdk/lib/_internal/compiler/implementation/scanner/scanner.dart
diff --git a/dart/sdk/lib/_internal/compiler/implementation/scanner/scanner.dart b/dart/sdk/lib/_internal/compiler/implementation/scanner/scanner.dart
index 0ad4dd591e2ff6b37fec26ec097934081d7615c6..c7e1ae74bfc80dd66e18131e89f74ad31601bcad 100644
--- a/dart/sdk/lib/_internal/compiler/implementation/scanner/scanner.dart
+++ b/dart/sdk/lib/_internal/compiler/implementation/scanner/scanner.dart
@@ -200,7 +200,7 @@ abstract class AbstractScanner implements Scanner {
       if (atEndOfFile()) {
         appendEofToken();
       } else {
-        error('Unexpected $EOF byte in input.');
+        error('Unexpected ${$EOF} byte in input.');
       }
     }