Export emojis.dart (dart-lang/markdown#377)

pkgs/markdown/lib/markdown.dart

diff --git a/pkgs/markdown/lib/markdown.dart b/pkgs/markdown/lib/markdown.dart
index b179fe0..06141cd 100644
--- a/pkgs/markdown/lib/markdown.dart
+++ b/pkgs/markdown/lib/markdown.dart
@@ -10,6 +10,7 @@
 export 'src/ast.dart';
 export 'src/block_parser.dart';
 export 'src/document.dart';
+export 'src/emojis.dart';
 export 'src/extension_set.dart';
 export 'src/html_renderer.dart';
 export 'src/inline_parser.dart';