patch 8.1.2177: Dart files are not recognized

Problem:    Dart files are not recognized.
Solution:   Add a filetype rule. (Eugene Ciurana, closes #5087)
diff --git a/src/version.c b/src/version.c
index 3a7347c..f96160e 100644
--- a/src/version.c
+++ b/src/version.c
@@ -742,6 +742,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    2177,
+/**/
     2176,
 /**/
     2175,