patch 9.1.0550: filetype: antlr4 files are not recognized

Problem:  filetype: antlr4 files are not recognized
Solution: Detect '*.g4' as antlr4 filetype, include a simple antlr4
          syntax and filetype plugin (Yinzuo Jiang)

closes: #15191

Signed-off-by: Yinzuo Jiang <jiangyinzuo@foxmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/version.c b/src/version.c
index dd5b254..caa779c 100644
--- a/src/version.c
+++ b/src/version.c
@@ -705,6 +705,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    550,
+/**/
     549,
 /**/
     548,