patch 9.0.2079: Not all Dart files detected

Problem:  Not all Dart files detected
Solution: Add shebang filetype detection for Dart

closes: #13449

Signed-off-by: Doug Kearns <dougkearns@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/runtime/autoload/dist/script.vim b/runtime/autoload/dist/script.vim
index fd7b8e0..8de8296 100644
--- a/runtime/autoload/dist/script.vim
+++ b/runtime/autoload/dist/script.vim
@@ -221,6 +221,10 @@
   elseif name =~ '^janet\>'
     return 'janet'
 
+    # Dart
+  elseif name =~ '^dart\>'
+    return 'dart'
+
   endif
 
   return ''